Strings and Regular Expressions
1 Introduction
Load packages:
library(tidyverse)
library(stringr) # package for manipulating strings (part of tidyverse)
library(lubridate) # package for working with dates and times
library(rvest) # package for reading and manipulating HTMLResources used to create this lecture:
- https://r4ds.had.co.nz/strings.html
- https://www.tutorialspoint.com/r/r_strings.htm
- https://swcarpentry.github.io/r-novice-inflammation/13-supp-data-structures/
- https://www.statmethods.net/input/datatypes.html
- https://www.stat.berkeley.edu/~s133/dates.html
1.1 Dataset we will use
We will use rtweet to pull Twitter data from the PAC-12 universities. We will use the university admissions Twitter handle if there is one, or the main Twitter handle for the university if there isn’t one:
# library(rtweet)
#
# p12 <- c("uaadmissions", "FutureSunDevils", "caladmissions", "UCLAAdmission",
# "futurebuffs", "uoregon", "BeaverVIP", "USCAdmission",
# "engagestanford", "UtahAdmissions", "UW", "WSUPullman")
# p12_full_df <- search_tweets(paste0("from:", p12, collapse = " OR "), n = 500)
#
# saveRDS(p12_full_df, "p12_dataset.RDS")
# Load previously pulled Twitter data
# p12_full_df <- readRDS("p12_dataset.RDS")
p12_full_df <- readRDS(url("https://github.com/anyone-can-cook/rclass2/raw/master/data/recruiting/p12_dataset.RDS", "rb"))
glimpse(p12_full_df)## Observations: 328
## Variables: 90
## $ user_id <chr> "22080148", "22080148", "22080148", "220…
## $ status_id <chr> "1254177694599675904", "1253431405993840…
## $ created_at <dttm> 2020-04-25 22:37:18, 2020-04-23 21:11:4…
## $ screen_name <chr> "WSUPullman", "WSUPullman", "WSUPullman"…
## $ text <chr> "Big Dez is headed to Indy!\n\n#GoCougs …
## $ source <chr> "Twitter for iPhone", "Twitter Web App",…
## $ display_text_width <dbl> 125, 58, 246, 83, 56, 64, 156, 271, 69, …
## $ reply_to_status_id <chr> NA, NA, NA, NA, NA, NA, NA, NA, "1252615…
## $ reply_to_user_id <chr> NA, NA, NA, NA, NA, NA, NA, NA, "2208014…
## $ reply_to_screen_name <chr> NA, NA, NA, NA, NA, NA, NA, NA, "WSUPull…
## $ is_quote <lgl> FALSE, FALSE, FALSE, FALSE, FALSE, FALSE…
## $ is_retweet <lgl> TRUE, FALSE, FALSE, FALSE, FALSE, FALSE,…
## $ favorite_count <int> 0, 322, 30, 55, 186, 53, 22, 44, 11, 0, …
## $ retweet_count <int> 230, 32, 1, 5, 0, 3, 2, 6, 2, 6, 3, 4, 5…
## $ quote_count <int> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ reply_count <int> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ hashtags <list> [<"GoCougs", "NFLDraft2020", "NFLCougs"…
## $ symbols <list> [NA, NA, NA, NA, NA, NA, NA, NA, NA, NA…
## $ urls_url <list> [NA, NA, NA, NA, NA, NA, NA, "commencem…
## $ urls_t.co <list> [NA, NA, NA, NA, NA, NA, NA, "https://t…
## $ urls_expanded_url <list> [NA, NA, NA, NA, NA, NA, NA, "https://c…
## $ media_url <list> ["http://pbs.twimg.com/ext_tw_video_thu…
## $ media_t.co <list> ["https://t.co/NdGsvXnij7", "https://t.…
## $ media_expanded_url <list> ["https://twitter.com/WSUCougarFB/statu…
## $ media_type <list> ["photo", "photo", "photo", "photo", "p…
## $ ext_media_url <list> ["http://pbs.twimg.com/ext_tw_video_thu…
## $ ext_media_t.co <list> ["https://t.co/NdGsvXnij7", "https://t.…
## $ ext_media_expanded_url <list> ["https://twitter.com/WSUCougarFB/statu…
## $ ext_media_type <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ mentions_user_id <list> [<"1250265324", "1409024796", "18088404…
## $ mentions_screen_name <list> [<"WSUCougarFB", "dadpat7", "Colts">, N…
## $ lang <chr> "en", "en", "en", "en", "en", "en", "en"…
## $ quoted_status_id <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_text <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_created_at <dttm> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,…
## $ quoted_source <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_favorite_count <int> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_retweet_count <int> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_user_id <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_screen_name <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_name <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_followers_count <int> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_friends_count <int> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_statuses_count <int> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_location <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_description <chr> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ quoted_verified <lgl> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ retweet_status_id <chr> "1254159118996127746", NA, NA, NA, NA, N…
## $ retweet_text <chr> "Big Dez is headed to Indy!\n\n#GoCougs …
## $ retweet_created_at <dttm> 2020-04-25 21:23:29, NA, NA, NA, NA, NA…
## $ retweet_source <chr> "Twitter for iPhone", NA, NA, NA, NA, NA…
## $ retweet_favorite_count <int> 1402, NA, NA, NA, NA, NA, NA, NA, NA, 26…
## $ retweet_retweet_count <int> 230, NA, NA, NA, NA, NA, NA, NA, NA, 6, …
## $ retweet_user_id <chr> "1250265324", NA, NA, NA, NA, NA, NA, NA…
## $ retweet_screen_name <chr> "WSUCougarFB", NA, NA, NA, NA, NA, NA, N…
## $ retweet_name <chr> "Washington State Football", NA, NA, NA,…
## $ retweet_followers_count <int> 77527, NA, NA, NA, NA, NA, NA, NA, NA, 9…
## $ retweet_friends_count <int> 1448, NA, NA, NA, NA, NA, NA, NA, NA, 31…
## $ retweet_statuses_count <int> 15363, NA, NA, NA, NA, NA, NA, NA, NA, 1…
## $ retweet_location <chr> "Pullman, WA", NA, NA, NA, NA, NA, NA, N…
## $ retweet_description <chr> "Official Twitter home of Washington Sta…
## $ retweet_verified <lgl> TRUE, NA, NA, NA, NA, NA, NA, NA, NA, FA…
## $ place_url <chr> NA, NA, NA, NA, NA, "https://api.twitter…
## $ place_name <chr> NA, NA, NA, NA, NA, "Pullman", NA, NA, N…
## $ place_full_name <chr> NA, NA, NA, NA, NA, "Pullman, WA", NA, N…
## $ place_type <chr> NA, NA, NA, NA, NA, "city", NA, NA, NA, …
## $ country <chr> NA, NA, NA, NA, NA, "United States", NA,…
## $ country_code <chr> NA, NA, NA, NA, NA, "US", NA, NA, NA, NA…
## $ geo_coords <list> [<NA, NA>, <NA, NA>, <NA, NA>, <NA, NA>…
## $ coords_coords <list> [<NA, NA>, <NA, NA>, <NA, NA>, <NA, NA>…
## $ bbox_coords <list> [<NA, NA, NA, NA, NA, NA, NA, NA>, <NA,…
## $ status_url <chr> "https://twitter.com/WSUPullman/status/1…
## $ name <chr> "WSU Pullman", "WSU Pullman", "WSU Pullm…
## $ location <chr> "Pullman, Washington USA", "Pullman, Was…
## $ description <chr> "We are an award-winning research univer…
## $ url <chr> "http://t.co/VxKZH9BuMS", "http://t.co/V…
## $ protected <lgl> FALSE, FALSE, FALSE, FALSE, FALSE, FALSE…
## $ followers_count <int> 43914, 43914, 43914, 43914, 43914, 43914…
## $ friends_count <int> 9717, 9717, 9717, 9717, 9717, 9717, 9717…
## $ listed_count <int> 556, 556, 556, 556, 556, 556, 556, 556, …
## $ statuses_count <int> 15234, 15234, 15234, 15234, 15234, 15234…
## $ favourites_count <int> 20124, 20124, 20124, 20124, 20124, 20124…
## $ account_created_at <dttm> 2009-02-26 23:39:34, 2009-02-26 23:39:3…
## $ verified <lgl> TRUE, TRUE, TRUE, TRUE, TRUE, TRUE, TRUE…
## $ profile_url <chr> "http://t.co/VxKZH9BuMS", "http://t.co/V…
## $ profile_expanded_url <chr> "http://www.wsu.edu", "http://www.wsu.ed…
## $ account_lang <lgl> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, …
## $ profile_banner_url <chr> "https://pbs.twimg.com/profile_banners/2…
## $ profile_background_url <chr> "http://abs.twimg.com/images/themes/them…
## $ profile_image_url <chr> "http://pbs.twimg.com/profile_images/576…p12_df <- p12_full_df %>% select("user_id", "created_at", "screen_name", "text", "location")
head(p12_df)## # A tibble: 6 x 5
## user_id created_at screen_name text location
## <chr> <dttm> <chr> <chr> <chr>
## 1 22080148 2020-04-25 22:37:18 WSUPullman "Big Dez is headed … Pullman, W…
## 2 22080148 2020-04-23 21:11:49 WSUPullman Cougar Cheese. That… Pullman, W…
## 3 22080148 2020-04-21 04:00:00 WSUPullman "Darien McLaughlin … Pullman, W…
## 4 22080148 2020-04-24 03:00:00 WSUPullman 6 houses, one pick.… Pullman, W…
## 5 22080148 2020-04-20 19:00:21 WSUPullman Why did you choose … Pullman, W…
## 6 22080148 2020-04-20 02:20:01 WSUPullman Tell us one of your… Pullman, W…2 Data structures and types
What is an object?
- Everything in R is an object
- We can classify objects based on their class and type
- The class of the object determines what kind of functions we can apply to it
- Objects may be combined to form data structures
Credit: R for Data Science
Basic data structures:
Basic data types:
- Logical (
TRUE,FALSE) - Numeric (e.g.,
5,2.5) - Integer (e.g.,
1L,4L, whereLtells R to store asintegertype) - Character (e.g.,
"R is fun")
Functions for investigating R objects (From Data Types and Structures)
str(): Compactly display the internal structure of an R objectclass(): What kind of object is it (high-level)?typeof(): What is the object’s data type (low-level)?
2.1 Atomtic vectors
What are atomic vectors?
- Atomic vectors are objects that contains elements
- Elements must be of the same data type (i.e., homogeneous)
- The
class()andtypeof()a vector describes the elements it contains
Example: Investigating logical vectors
## logi [1:4] TRUE FALSE FALSE TRUE## [1] "logical"## [1] "logical"Example: Investigating numeric vectors
## num [1:4] 1 3 5 7## [1] "numeric"## [1] "double"Example: Investigating integer vectors
## int [1:4] 1 3 5 7## [1] "integer"## [1] "integer"2.2 Lists
What are lists?
- Lists are objects that contains elements
- Elements do not need to be of the same type (i.e., heterogeneous)
- Elements can be atomic vectors or even other lists
- The
class()andtypeof()a list islist
Example: Investigating heterogeneous lists
## List of 4
## $ : num 2.5
## $ : chr "abc"
## $ : logi TRUE
## $ : int [1:3] 1 2 3## [1] "list"## [1] "list"Example: Investigating nested lists
## List of 3
## $ :List of 3
## ..$ : logi TRUE
## ..$ : num [1:3] 1 2 3
## ..$ :List of 1
## .. ..$ : chr [1:3] "a" "b" "c"
## $ : logi FALSE
## $ : int 10## [1] "list"## [1] "list"2.2.1 Dataframes
What are dataframes?
- Dataframes are a special kind of list with the following characteristics:
- Each element is a vector (i.e., a column in the dataframe)
- The element should be named (i.e., column name in the dataframe)
- Each of the vectors must be the same length (i.e., same number of rows in the dataframe)
- The data type of each vector may be different
- Dataframes can be created using the function
data.frame() - The
class()of a dataframe isdata.frame - The
typeof()a dataframe islist
Example: Investigating dataframe
df <- data.frame(
colA = c(1, 2, 3),
colB = c("a", "b", "c"),
colC = c(TRUE, FALSE, TRUE),
stringsAsFactors = FALSE
)
df## # A tibble: 3 x 3
## colA colB colC
## <dbl> <chr> <lgl>
## 1 1 a TRUE
## 2 2 b FALSE
## 3 3 c TRUE## 'data.frame': 3 obs. of 3 variables:
## $ colA: num 1 2 3
## $ colB: chr "a" "b" "c"
## $ colC: logi TRUE FALSE TRUE## [1] "data.frame"## [1] "list"2.3 Converting between classes
Functions for converting between classes:
as.logical(): Convert tologicalas.numeric(): Convert tonumericas.integer(): Convert tointegeras.character(): Convert tocharacteras.list(): Convert tolistas.data.frame(): Convert todata.frame
Example: Using
as.logical() to convert to logical
Character vector coerced to logical vector:
# Only "TRUE"/"FALSE", "True"/"False", "T"/"F", "true"/"false" are able to be coerced to logical type
as.logical(c("TRUE", "FALSE", "True", "False", "true", "false", "T", "F", "t", "f", ""))## [1] TRUE FALSE TRUE FALSE TRUE FALSE TRUE FALSE NA NA NANumeric vector coerced to logical vector:
# 0 is treated as FALSE, while all other numeric values are treated as TRUE
as.logical(c(0, 0.0, 1, -1, 20, 5.5))## [1] FALSE FALSE TRUE TRUE TRUE TRUEExample: Using
as.numeric() to convert to numeric
Logical vector coerced to numeric vector:
## [1] 0 1Character vector coerced to numeric vector:
# Strings containing numeric values can be coerced to numeric (leading 0's are dropped)
# All other characters become NA
as.numeric(c("0", "007", "2.5", "abc", "."))## [1] 0.0 7.0 2.5 NA NAExample: Using
as.integer() to convert to integer
Logical vector coerced to integer vector:
## [1] 0 1Character vector coerced to integer vector:
# Strings containing numeric values can be coerced to integer (leading 0's are dropped, decimals are truncated)
# All other characters become NA
as.integer(c("0", "007", "2.5", "abc", "."))## [1] 0 7 2 NA NANumeric vector coerced to integer vector:
## [1] 0 2 10 8 -1Example: Using
as.character() to convert to character
Logical vector coerced to character vector:
## [1] "FALSE" "TRUE"Numeric vector coerced to character vector:
## [1] "-5" "0" "2.5"Integer vector coerced to character vector:
## [1] "-2" "0" "10"Example: Using
as.list() to convert to list
Atomic vectors coerced to list:
## [[1]]
## [1] TRUE
##
## [[2]]
## [1] FALSE## [[1]]
## [1] "a"
##
## [[2]]
## [1] "b"
##
## [[3]]
## [1] "c"## [[1]]
## [1] 1
##
## [[2]]
## [1] 2
##
## [[3]]
## [1] 3Example: Using
as.data.frame() to convert to data.frame
Lists coerced to dataframe:
## List of 2
## $ A: chr [1:3] "x" "y" "z"
## $ B: num [1:3] 1 2 3## 'data.frame': 3 obs. of 2 variables:
## $ A: chr "x" "y" "z"
## $ B: num 1 2 33 String basics
What are strings?
- String is a type of data in R
- You can create strings using either single quotes (
') or double quotes (")- Internally, R stores strings using double quotes
- The
class()andtypeof()a string ischaracter
Example: Creating string using single quotes
Notice how R stores strings using double quotes internally:
## [1] "This is a string"
Example: Creating string using double quotes
## [1] "Strings can also contain numbers: 123"
Example: Checking class and type of strings
## [1] "character"## [1] "character"3.1 Special Characters
“A sequence in a string that starts with a
\is called an escape sequence and allows us to include special characters in our strings.”
Credit: Escape sequences from DataCamp
Common special characters:
\': literal single quote\": literal double quote\\: literal backslash\n: newline\t: tab
These characters followed by a backslash \ take on a new meaning. The n by itself is just an n. When you add a backslash to the \n you are escaping it and making it a special character where \n now represents a newline.
The writeLines() function:
?writeLines
# SYNTAX AND DEFAULT VALUES
writeLines(text, con = stdout(), sep = "\n", useBytes = FALSE)- “
writeLines()displays quotes and backslashes as they would be read, rather than as R stores them.” (From writeLines documentation) - When we include escape sequences in the string, it is helpful to use
writeLines()to see how the escaped string looks writeLines()will also output the string without showing the outer pair of double quotes that R uses to store it, so we only see the content of the string
Example: Escaping single quotes
## [1] "Escaping single quote ' within single quotes"Alternatively, we could’ve just created the string using double quotes:
## [1] "Single quote ' within double quotes does not need escaping"Using writeLines() shows us only the content of the string without the outer pair of double quotes that R uses to store strings:
## Single quote ' within double quotes does not need escapingExample: Escaping double quotes
## [1] "Escaping double quote \" within double quotes"Alternatively, we could’ve just created the string using single quotes:
## [1] "Double quote \" within single quotes does not need escaping"Notice how the backslash still showed up in the above output to escape our double quote from the outer pair of double quotes that R uses to store the string. This is no longer an issue if we use writeLines() to only show the string content:
## Double quote " within single quotes does not need escapingExample: Escaping double quotes within double quotes
## [1] "I called my mom and she said \"Echale ganas!\""Using writeLines() shows us only the content of the string without the backslashes:
## I called my mom and she said "Echale ganas!"Example: Escaping backslashes
To include a literal backslash in the string, we need to escape the backslash with another backslash:
## [1] "The executable is located in C:\\Program Files\\Git\\bin"Use writeLines() to see the escaped string:
## The executable is located in C:\Program Files\Git\binExample: Other special characters
## [1] "A\tB\nC\tD"Use writeLines() to see the escaped string:
## A B
## C D3.1.1 Escape special characters using Twitter data
Let’s take a look at some tweets from our PAC-12 universities.
- Let’s start by grabbing observations 1-3 from the
textcolumn.
## [1] "Big Dez is headed to Indy!\n\n#GoCougs | #NFLDraft2020 | @dadpat7 | @Colts | #NFLCougs https://t.co/NdGsvXnij7"
## [2] "Cougar Cheese. That's it. That's the tweet. \U0001f9c0#WSU #GoCougs https://t.co/0OWGvQlRZs"
## [3] "Darien McLaughlin '19, and her dog, Yuki, went on a #Pullman distance walk this weekend. We will let you judge who was leading the way.\U0001f6b6♀️\U0001f415\n\nTweet a pic of how you are social distancing w/ the hashtag #CougsContain & tag @WSUPullman #GoCougs https://t.co/EltXDy1tPt"- Using
writeLines()we can see the contents of the strings as they would be read, rather than as R stores them.
## Big Dez is headed to Indy!
##
## #GoCougs | #NFLDraft2020 | @dadpat7 | @Colts | #NFLCougs https://t.co/NdGsvXnij7
## Cougar Cheese. That's it. That's the tweet. 🧀#WSU #GoCougs https://t.co/0OWGvQlRZs
## Darien McLaughlin '19, and her dog, Yuki, went on a #Pullman distance walk this weekend. We will let you judge who was leading the way.🚶♀️🐕
##
## Tweet a pic of how you are social distancing w/ the hashtag #CougsContain & tag @WSUPullman #GoCougs https://t.co/EltXDy1tPtExample: Escaping double quotes using Twitter data
Using Twitter data you may encounter a lot of strings with double quotes.
- In the example below, our string includes special characters
\"and\nto escape the double quotes and the newline character.
- In the example below, our string includes special characters
## [1] "\"I really am glad that inside Engineering Student Services, I’ve been able to connect with my ESS advisor and professional development advisors there.\"\n-Alexandro Garcia, Civil & Environmental Engineering, 3rd year\n#imaberkeleyengineer #iamberkeley #voicesofberkeleyengineering https://t.co/ToVEynIUWH"Using
writeLines()we can see the contents of the strings as they would be read, rather than as R stores them.- We no longer see the escaped characters
\"or\n
- We no longer see the escaped characters
## "I really am glad that inside Engineering Student Services, I’ve been able to connect with my ESS advisor and professional development advisors there."
## -Alexandro Garcia, Civil & Environmental Engineering, 3rd year
## #imaberkeleyengineer #iamberkeley #voicesofberkeleyengineering https://t.co/ToVEynIUWH4 stringr package
“A consistent, simple and easy to use set of wrappers around the fantastic
stringipackage. All function and argument names (and positions) are consistent, all functions deal withNA’s and zero length vectors in the same way, and the output from one function is easy to feed into the input of another.”
Credit: stringr R documentation
The stringr package:
- The
stringrpackage is based off thestringipackage and is part of Tidyverse stringrcontains functions to work with strings- For many functions in the
stringrpackage, there are equivalent “base R” functions - But
stringrfunctions all follow the same rules, while rules often differ across different “base R” string functions, so we will focus exclusively onstringrfunctions - Most
stringrfunctions start withstr_(e.g.,str_length)
4.1 str_length()
The str_length() function:
- Function: Find string length
- Arguments:
string: Character vector (or vector coercible to character)
- Note that
str_length()calculates the length of a string, whereas thelength()function (which is not part ofstringrpackage) calculates the number of elements in an object
Example: Using
str_length() on string
## [1] 4Compare to length(), which treats the string as a single object:
## [1] 1Example: Using
str_length() on character vector
## [1] 4 2 3Compare to length(), which finds the number of elements in the vector:
## [1] 3Example: Using
str_length() on other vectors coercible to character
Logical vectors can be coerced to character vectors:
## [1] 4 5Numeric vectors can be coerced to character vectors:
## [1] 1 3 4Integer vectors can be coerced to character vectors:
## [1] 1 3Example: Using
str_length() on dataframe column
Recall that the columns in a dataframe are just vectors, so we can use str_length() as long as the vector is coercible to character type. Let’s look at the screen_name column from the p12_df:
## Classes 'tbl_df', 'tbl' and 'data.frame': 328 obs. of 5 variables:
## $ user_id : chr "22080148" "22080148" "22080148" "22080148" ...
## $ created_at : POSIXct, format: "2020-04-25 22:37:18" "2020-04-23 21:11:49" ...
## $ screen_name: chr "WSUPullman" "WSUPullman" "WSUPullman" "WSUPullman" ...
## $ text : chr "Big Dez is headed to Indy!\n\n#GoCougs | #NFLDraft2020 | @dadpat7 | @Colts | #NFLCougs https://t.co/NdGsvXnij7" "Cougar Cheese. That's it. That's the tweet. \U0001f9c0#WSU #GoCougs https://t.co/0OWGvQlRZs" "Darien McLaughlin '19, and her dog, Yuki, went on a #Pullman distance walk this weekend. We will let you judge "| __truncated__ "6 houses, one pick. Cougs, which one you got? Reply \u2b07️ #WSU #CougsContain #GoCougs https://t.co/lNDx7r71b2" ...
## $ location : chr "Pullman, Washington USA" "Pullman, Washington USA" "Pullman, Washington USA" "Pullman, Washington USA" ...## chr [1:328] "WSUPullman" "WSUPullman" "WSUPullman" "WSUPullman" ...
[Base R method] Use str_length() to calculate the length of each screen_name:
## [1] "WSUPullman" "CalAdmissions" "UW"
## [4] "USCAdmission" "uoregon" "FutureSunDevils"
## [7] "UCLAAdmission" "UtahAdmissions" "futurebuffs"
## [10] "uaadmissions" "BeaverVIP"## [1] 10 13 2 12 7 15 13 14 11 12 9
[Tidyverse method] Use str_length() to calculate the length of each screen_name:
## # A tibble: 11 x 1
## screen_name
## <chr>
## 1 WSUPullman
## 2 CalAdmissions
## 3 UW
## 4 USCAdmission
## 5 uoregon
## 6 FutureSunDevils
## 7 UCLAAdmission
## 8 UtahAdmissions
## 9 futurebuffs
## 10 uaadmissions
## 11 BeaverVIP## Warning in stri_length(string): argument is not an atomic vector; coercing## [1] 163Notice that the above line does not work as expected because we passed in a dataframe to str_length() and it is trying to coerce that to character:
## [1] "tbl_df" "tbl" "data.frame"An alternative way is to add a column to the dataframe that contains the result of applying str_length() to the screen_name vector:
## # A tibble: 11 x 2
## screen_name screen_name_len
## <chr> <int>
## 1 WSUPullman 10
## 2 CalAdmissions 13
## 3 UW 2
## 4 USCAdmission 12
## 5 uoregon 7
## 6 FutureSunDevils 15
## 7 UCLAAdmission 13
## 8 UtahAdmissions 14
## 9 futurebuffs 11
## 10 uaadmissions 12
## 11 BeaverVIP 94.2 str_c()
The str_c() function:
- Function: Concatenate strings between vectors (element-wise)
- Arguments:
- The input is one or more character vectors (or vectors coercible to character)
- Zero length arguments are removed
- Short arguments are recycled to the length of the longest
sep: String to insert between input vectorscollapse: Optional string used to combine input vectors into single string
- The input is one or more character vectors (or vectors coercible to character)
Example: Using
str_c() on strings
Each string input is treated as a character vector of size 1:
## [1] "abc"We can use sep to specify how the elements are separated:
## [1] "a~b~c"Note that we can also use any other input that can be coerced to character:
## [1] "TRUE1.52X"Example: Using
str_c() on single vector
Since we only provided one input vector, each individual element has nothing to concatenate with:
## [1] "a" "b" "c"But we can still specify the collapse argument to collapse the elements to a single string:
## [1] "a|b|c"Example: Using
str_c() on multiple vectors
When multiple vectors are provided, they are joined together element-wise, recycling the elements of the shorter vectors:
## [1] "#a1TRUE" "#b2FALSE" "#c3TRUE" "#d1FALSE"We can specify sep and collapse:
## [1] "#~a~1~TRUE|#~b~2~FALSE|#~c~3~TRUE|#~d~1~FALSE"Example: Using
str_c() on dataframe columns
Let’s combine the user_id and screen_name columns from p12_df. We’ll focus on unique Twitter handles:
## # A tibble: 11 x 2
## user_id screen_name
## <chr> <chr>
## 1 22080148 WSUPullman
## 2 15988549 CalAdmissions
## 3 27103822 UW
## 4 198643896 USCAdmission
## 5 40940457 uoregon
## 6 325014504 FutureSunDevils
## 7 2938776590 UCLAAdmission
## 8 4922145709 UtahAdmissions
## 9 45879674 futurebuffs
## 10 44733626 uaadmissions
## 11 403743606 BeaverVIP
[Base R method] Use str_c() to combine user_id and screen_name:
## [1] "22080148 = WSUPullman, 15988549 = CalAdmissions, 27103822 = UW, 198643896 = USCAdmission, 40940457 = uoregon, 325014504 = FutureSunDevils, 2938776590 = UCLAAdmission, 4922145709 = UtahAdmissions, 45879674 = futurebuffs, 44733626 = uaadmissions, 403743606 = BeaverVIP"
[Tidyverse method] Use str_c() to combine user_id and screen_name:
## # A tibble: 11 x 3
## user_id screen_name twitter_handle
## <chr> <chr> <chr>
## 1 22080148 WSUPullman User #22080148 is @WSUPullman
## 2 15988549 CalAdmissions User #15988549 is @CalAdmissions
## 3 27103822 UW User #27103822 is @UW
## 4 198643896 USCAdmission User #198643896 is @USCAdmission
## 5 40940457 uoregon User #40940457 is @uoregon
## 6 325014504 FutureSunDevils User #325014504 is @FutureSunDevils
## 7 2938776590 UCLAAdmission User #2938776590 is @UCLAAdmission
## 8 4922145709 UtahAdmissions User #4922145709 is @UtahAdmissions
## 9 45879674 futurebuffs User #45879674 is @futurebuffs
## 10 44733626 uaadmissions User #44733626 is @uaadmissions
## 11 403743606 BeaverVIP User #403743606 is @BeaverVIP4.3 str_sub()
The str_sub() function:
?str_sub
# SYNTAX AND DEFAULT VALUES
str_sub(string, start = 1L, end = -1L)
str_sub(string, start = 1L, end = -1L, omit_na = FALSE) <- value- Function: Subset strings
- Arguments:
string: Character vector (or vector coercible to character)start: Position of first character to be included in substring (default:1)end: Position of last character to be included in substring (default:-1)- Negative index means counting backwards from the end of the string
- If an element in the vector is shorter than the specified
end, it will just include all the available characters that it does have
omit_na: IfTRUE, missing values in any of the arguments provided will result in an unchanged input
- When
str_sub()is used in the assignment form, you can replace the subsetted part of the string with avalueof your choice- If an element in the vector is too short to meet the subset specification, the replacement
valuewill be concatenated to the end of that element - Note that this modifies your input vector directly, so you must have the vector saved to a variable (see example below)
- If an element in the vector is too short to meet the subset specification, the replacement
Example: Using
str_sub() to subset strings
If no start and end positions are specified, str_sub() will by default return the entire (original) string:
## [1] "abcdefg" "123" "TRUE"Note that if an element is shorter than the specified end (i.e., 123 in the example below), it will just include all the available characters that it does have:
## [1] "bcd" "23" "RUE"Remember we can also use negative index to count the position starting from the back:
## [1] "bcdef" "2" "RU"Example: Using
str_sub() to replace strings
If no start and end positions are specified, str_sub() will by default return the original string, so the entire string would be replaced:
## [1] "*" "*" "*" "*" "*"If an element in the vector is too short to meet the subset specification, the replacement value will be concatenated to the end of that element:
## [1] "A*" "A*" "A*" "A*D" "A*DE"Note that because the replacement form of str_sub() modifies the input vector directly, we need to save it in a variable first. Directly passing in the vector to str_sub() would give us an error:
Example: Using
str_sub() on dataframe column
We can use as.character() to turn the created_at value to a string, then use str_sub() to extract out various date/time components from the string:
p12_datetime_df <- p12_df %>% select(created_at) %>%
mutate(
dt_chr = as.character(created_at),
date_chr = str_sub(dt_chr, 1, 10),
yr_chr = str_sub(dt_chr, 1, 4),
mth_chr = str_sub(dt_chr, 6, 7),
day_chr = str_sub(dt_chr, 9, 10),
hr_chr = str_sub(dt_chr, -8, -7),
min_chr = str_sub(dt_chr, -5, -4),
sec_chr = str_sub(dt_chr, -2, -1)
)
p12_datetime_df## # A tibble: 328 x 9
## created_at dt_chr date_chr yr_chr mth_chr day_chr hr_chr
## <dttm> <chr> <chr> <chr> <chr> <chr> <chr>
## 1 2020-04-25 22:37:18 2020-… 2020-04… 2020 04 25 22
## 2 2020-04-23 21:11:49 2020-… 2020-04… 2020 04 23 21
## 3 2020-04-21 04:00:00 2020-… 2020-04… 2020 04 21 04
## 4 2020-04-24 03:00:00 2020-… 2020-04… 2020 04 24 03
## 5 2020-04-20 19:00:21 2020-… 2020-04… 2020 04 20 19
## 6 2020-04-20 02:20:01 2020-… 2020-04… 2020 04 20 02
## 7 2020-04-22 04:00:00 2020-… 2020-04… 2020 04 22 04
## 8 2020-04-25 17:00:00 2020-… 2020-04… 2020 04 25 17
## 9 2020-04-21 15:13:06 2020-… 2020-04… 2020 04 21 15
## 10 2020-04-21 17:52:47 2020-… 2020-04… 2020 04 21 17
## # … with 318 more rows, and 2 more variables: min_chr <chr>, sec_chr <chr>4.4 Other stringr functions
Other useful stringr functions:
str_to_upper(): Turn strings to uppercasestr_to_lower(): Turn strings to lowercasestr_sort(): Sort a character vectorstr_trim(): Trim whitespace from strings (including\n,\t, etc.)str_pad(): Pad strings with specified character
Example: Using
str_to_upper() to turn strings to uppercase
Turn column names of p12_df to uppercase:
## [1] "user_id" "created_at" "screen_name" "text" "location"## [1] "USER_ID" "CREATED_AT" "SCREEN_NAME" "TEXT" "LOCATION"Example: Using
str_to_lower() to turn strings to lowercase
Turn column names of p12_df to lowercase:
## [1] "USER_ID" "CREATED_AT" "SCREEN_NAME" "TEXT" "LOCATION"## [1] "user_id" "created_at" "screen_name" "text" "location"Example: Using
str_sort() to sort character vector
Sort the vector of p12_df column names:
## [1] "user_id" "created_at" "screen_name" "text" "location"## [1] "created_at" "location" "screen_name" "text" "user_id"## [1] "user_id" "text" "screen_name" "location" "created_at"Example: Using
str_trim() to trim whitespace from string
## [1] "ABC" "XYZ"## [1] "ABC " "XYZ\t"## [1] "\nABC" " XYZ"Example: Using
str_pad() to pad string with character
Let’s say we have a vector of zip codes that has lost all leading 0’s. We can use str_pad() to add that back in:
# Pad the left side of strings with "0" until width of 5 is reached
str_pad(c(95035, 90024, 5009, 5030), width = 5, side = "left", pad = "0")## [1] "95035" "90024" "05009" "05030"5 Dates and times
“Date-time data can be frustrating to work with in R. R commands for date-times are generally unintuitive and change depending on the type of date-time object being used. Moreover, the methods we use with date-times must be robust to time zones, leap days, daylight savings times, and other time related quirks, and R lacks these capabilities in some situations. Lubridate makes it easier to do the things R does with date-times and possible to do the things R does not.”
Credit: lubridate documentation
How are dates and times stored in R? (From Dates and Times in R)
- The
Dateclass is used for storing dates- “Internally,
Dateobjects are stored as the number of days since January 1, 1970, using negative numbers for earlier dates. Theas.numeric()function can be used to convert aDateobject to its internal form.”
- “Internally,
- POSIX classes can be used for storing date plus times
- “The
POSIXctclass stores date/time values as the number of seconds since January 1, 1970” - “The
POSIXltclass stores date/time values as a list of components (hour, min, sec, mon, etc.) making it easy to extract these parts”
- “The
- There is no native R class for storing only time
Why use date/time objects?
- Using date/time objects makes it easier to fetch or modify various date/time components (e.g., year, month, day, day of the week)
- Compared to if the date/time is just stored in a string, these components are not as readily accessible and need to be parsed
- You can perform certain arithmetics with date/time objects (e.g., find the “difference” between date/time points)
5.1 Creating date/time objects
5.1.1 Creating date/time objects by parsing input
Functions that create date/time objects by parsing character or numeric input:
- Create
Dateobject:ymd(),ydm(),mdy(),myd(),dmy(),dym()ystands for year,mstands for month,dstands for day- Select the function that represents the order in which your date input is formatted, and the function will be able to parse your input and create a
Dateobject
- Create
POSIXctobject:ymd_h(),ymd_hm(),ymd_hms(), etc.hstands for hour,mstands for minute,sstands for second- For any of the previous 6 date functions, you can append
h,hm, orhmsif you want to provide additional time information in order to create aPOSIXctobject - To force a
POSIXctobject without providing any time information, you can just provide a timezone (usingtz) to one of the date functions and it will assume midnight as the time - You can use
Sys.timezone()to get the timezone for your location
Example: Creating
Date object from character or numeric input
The lubridate functions are flexible and can parse dates in various formats:
## [1] "2020-01-01"## [1] "2020-01-01"## [1] "2020-01-01"## [1] "2020-01-01"
Investigate the Date object:
## [1] "Date"## [1] "double"## [1] 18262Example: Creating
POSIXct object from character or numeric input
The lubridate functions are flexible and can parse AM/PM in various formats:
## [1] "2019-12-31 23:00:00 UTC"## [1] "2019-12-31 23:59:00 UTC"## [1] "2019-12-31 23:59:59 UTC"## [1] "2019-12-31 23:59:59 UTC"
Investigate the POSIXct object:
## [1] "POSIXct" "POSIXt"## [1] "double"## [1] 1577836799
We can also create a POSIXct object from a date function by providing a timezone. The time would default to midnight:
## [1] "2020-01-01 UTC"# Number of seconds since January 1, 1970
as.numeric(dt) # Note that this is indeed 1 sec after the previous example## [1] 1577836800Example: Creating
Date objects from dataframe column
Using the p12_datetime_df we created earlier, we can create Date objects from the date_chr column:
# Use `ymd()` to parse the string stored in the `date_chr` column
p12_datetime_df %>% select(created_at, dt_chr, date_chr) %>%
mutate(date_ymd = ymd(date_chr))## # A tibble: 328 x 4
## created_at dt_chr date_chr date_ymd
## <dttm> <chr> <chr> <date>
## 1 2020-04-25 22:37:18 2020-04-25 22:37:18 2020-04-25 2020-04-25
## 2 2020-04-23 21:11:49 2020-04-23 21:11:49 2020-04-23 2020-04-23
## 3 2020-04-21 04:00:00 2020-04-21 04:00:00 2020-04-21 2020-04-21
## 4 2020-04-24 03:00:00 2020-04-24 03:00:00 2020-04-24 2020-04-24
## 5 2020-04-20 19:00:21 2020-04-20 19:00:21 2020-04-20 2020-04-20
## 6 2020-04-20 02:20:01 2020-04-20 02:20:01 2020-04-20 2020-04-20
## 7 2020-04-22 04:00:00 2020-04-22 04:00:00 2020-04-22 2020-04-22
## 8 2020-04-25 17:00:00 2020-04-25 17:00:00 2020-04-25 2020-04-25
## 9 2020-04-21 15:13:06 2020-04-21 15:13:06 2020-04-21 2020-04-21
## 10 2020-04-21 17:52:47 2020-04-21 17:52:47 2020-04-21 2020-04-21
## # … with 318 more rowsExample: Creating
POSIXct objects from dataframe column
Using the p12_datetime_df we created earlier, we can recreate the created_at column (class POSIXct) from the dt_chr column (class character):
# Use `ymd_hms()` to parse the string stored in the `dt_chr` column
p12_datetime_df %>% select(created_at, dt_chr) %>%
mutate(datetime_ymd_hms = ymd_hms(dt_chr))## # A tibble: 328 x 3
## created_at dt_chr datetime_ymd_hms
## <dttm> <chr> <dttm>
## 1 2020-04-25 22:37:18 2020-04-25 22:37:18 2020-04-25 22:37:18
## 2 2020-04-23 21:11:49 2020-04-23 21:11:49 2020-04-23 21:11:49
## 3 2020-04-21 04:00:00 2020-04-21 04:00:00 2020-04-21 04:00:00
## 4 2020-04-24 03:00:00 2020-04-24 03:00:00 2020-04-24 03:00:00
## 5 2020-04-20 19:00:21 2020-04-20 19:00:21 2020-04-20 19:00:21
## 6 2020-04-20 02:20:01 2020-04-20 02:20:01 2020-04-20 02:20:01
## 7 2020-04-22 04:00:00 2020-04-22 04:00:00 2020-04-22 04:00:00
## 8 2020-04-25 17:00:00 2020-04-25 17:00:00 2020-04-25 17:00:00
## 9 2020-04-21 15:13:06 2020-04-21 15:13:06 2020-04-21 15:13:06
## 10 2020-04-21 17:52:47 2020-04-21 17:52:47 2020-04-21 17:52:47
## # … with 318 more rows5.1.2 Creating date/time objects from individual components
Functions that create date/time objects from various date/time components:
- Create
Dateobject:make_date()- Syntax and default values:
make_date(year = 1970L, month = 1L, day = 1L) - All inputs are coerced to integer
- Syntax and default values:
- Create
POSIXctobject:make_datetime()- Syntax and default values:
make_datetime(year = 1970L, month = 1L, day = 1L, hour = 0L, min = 0L, sec = 0, tz = "UTC")
- Syntax and default values:
Example: Creating
Date object from individual components
There are various ways to pass in the inputs to create the same Date object:
## [1] "2020-01-01"## [1] "2020-01-01"## [1] "2020-01-01"Example: Creating
POSIXct object from individual components
## [1] "2019-12-31 23:59:59 UTC"Example: Creating
Date objects from dataframe columns
Using the p12_datetime_df we created earlier, we can create Date objects from the various date component columns:
# Use `make_date()` to create a `Date` object from the `yr_chr`, `mth_chr`, `day_chr` fields
p12_datetime_df %>% select(created_at, dt_chr, yr_chr, mth_chr, day_chr) %>%
mutate(date_make_date = make_date(yr_chr, mth_chr, day_chr))## # A tibble: 328 x 6
## created_at dt_chr yr_chr mth_chr day_chr date_make_date
## <dttm> <chr> <chr> <chr> <chr> <date>
## 1 2020-04-25 22:37:18 2020-04-25 22… 2020 04 25 2020-04-25
## 2 2020-04-23 21:11:49 2020-04-23 21… 2020 04 23 2020-04-23
## 3 2020-04-21 04:00:00 2020-04-21 04… 2020 04 21 2020-04-21
## 4 2020-04-24 03:00:00 2020-04-24 03… 2020 04 24 2020-04-24
## 5 2020-04-20 19:00:21 2020-04-20 19… 2020 04 20 2020-04-20
## 6 2020-04-20 02:20:01 2020-04-20 02… 2020 04 20 2020-04-20
## 7 2020-04-22 04:00:00 2020-04-22 04… 2020 04 22 2020-04-22
## 8 2020-04-25 17:00:00 2020-04-25 17… 2020 04 25 2020-04-25
## 9 2020-04-21 15:13:06 2020-04-21 15… 2020 04 21 2020-04-21
## 10 2020-04-21 17:52:47 2020-04-21 17… 2020 04 21 2020-04-21
## # … with 318 more rowsExample: Creating
POSIXct objects from dataframe columns
Using the p12_datetime_df we created earlier, we can recreate the created_at column (class POSIXct) from the various date and time component columns (class character):
# Use `make_datetime()` to create a `POSIXct` object from the `yr_chr`, `mth_chr`, `day_chr`, `hr_chr`, `min_chr`, `sec_chr` fields
# Convert inputs to integers first
p12_datetime_df %>%
mutate(datetime_make_datetime = make_datetime(
as.integer(yr_chr), as.integer(mth_chr), as.integer(day_chr),
as.integer(hr_chr), as.integer(min_chr), as.integer(sec_chr)
)) %>%
select(datetime_make_datetime, yr_chr, mth_chr, day_chr, hr_chr, min_chr, sec_chr)## # A tibble: 328 x 7
## datetime_make_datetime yr_chr mth_chr day_chr hr_chr min_chr sec_chr
## <dttm> <chr> <chr> <chr> <chr> <chr> <chr>
## 1 2020-04-25 22:37:18 2020 04 25 22 37 18
## 2 2020-04-23 21:11:49 2020 04 23 21 11 49
## 3 2020-04-21 04:00:00 2020 04 21 04 00 00
## 4 2020-04-24 03:00:00 2020 04 24 03 00 00
## 5 2020-04-20 19:00:21 2020 04 20 19 00 21
## 6 2020-04-20 02:20:01 2020 04 20 02 20 01
## 7 2020-04-22 04:00:00 2020 04 22 04 00 00
## 8 2020-04-25 17:00:00 2020 04 25 17 00 00
## 9 2020-04-21 15:13:06 2020 04 21 15 13 06
## 10 2020-04-21 17:52:47 2020 04 21 17 52 47
## # … with 318 more rows5.2 Date/time object components
Storing data using date/time objects makes it easier to get and set the various date/time components.
- Basic accessor functions:
date(): Date componentyear(): Yearmonth(): Monthday(): Dayhour(): Hourminute(): Minutesecond(): Secondweek(): Week of the yearwday(): Day of the week (1for Sunday to7for Saturday)am(): Is it in the am? (returnsTRUEorFALSE)pm(): Is it in the pm? (returnsTRUEorFALSE)
- To get a date/time component, you can simply pass a date/time object to the function
- Syntax:
accessor_function(<date/time_object>)
- Syntax:
- To set a date/time component, you can assign into the accessor function to change the component
- Syntax:
accessor_function(<date/time_object>) <- "new_component" - Note that
am()andpm()can’t be set. Modify the time components instead.
- Syntax:
Example: Getting date/time components
## [1] "2019-12-31 23:59:59 UTC"## [1] "2019-12-31"## [1] 23## [1] TRUE## [1] 3Example: Setting date/time components
## [1] "2019-12-31 23:59:59 UTC"## [1] 53# Set week of year (move back 1 week)
week(dt) <- week(dt) - 1
# Date now moved from New Year's Eve to Christmas Eve
dt## [1] "2019-12-24 23:59:59 UTC"## [1] "2019-12-25 23:59:59 UTC"Example: Getting date/time components from dataframe column
Using the p12_datetime_df we created earlier, we can isolate the various date/time components from the POSIXct object in the created_at column:
# The extracted date/time components will be of numeric type
p12_datetime_df %>% select(created_at) %>%
mutate(
yr_num = year(created_at),
mth_num = month(created_at),
day_num = day(created_at),
hr_num = hour(created_at),
min_num = minute(created_at),
sec_num = second(created_at),
ampm = ifelse(am(created_at), 'AM', 'PM') # am()/pm() returns TRUE/FALSE
)## # A tibble: 328 x 8
## created_at yr_num mth_num day_num hr_num min_num sec_num ampm
## <dttm> <dbl> <dbl> <int> <int> <int> <dbl> <chr>
## 1 2020-04-25 22:37:18 2020 4 25 22 37 18 PM
## 2 2020-04-23 21:11:49 2020 4 23 21 11 49 PM
## 3 2020-04-21 04:00:00 2020 4 21 4 0 0 AM
## 4 2020-04-24 03:00:00 2020 4 24 3 0 0 AM
## 5 2020-04-20 19:00:21 2020 4 20 19 0 21 PM
## 6 2020-04-20 02:20:01 2020 4 20 2 20 1 AM
## 7 2020-04-22 04:00:00 2020 4 22 4 0 0 AM
## 8 2020-04-25 17:00:00 2020 4 25 17 0 0 PM
## 9 2020-04-21 15:13:06 2020 4 21 15 13 6 PM
## 10 2020-04-21 17:52:47 2020 4 21 17 52 47 PM
## # … with 318 more rows5.3 Time spans
3 ways to represent time spans (From lubridate cheatsheet)
- Intervals represent specific intervals of the timeline, bounded by start and end date-times
- Example: People with birthdays between the interval October 23 to November 22 are Scorpios
- Periods track changes in clock times, which ignore time line irregularities
- Example: Daylight savings time ends at the beginning of November and we gain an hour - this extra hour is ignored when determining the period between October 23 to November 22
- Durations track the passage of physical time, which deviates from clock time when irregularities occur
- Example: Daylight savings time ends at the beginning of November and we gain an hour - this extra hour is added when determining the duration between October 23 to November 22
5.3.1 Time spans using lubridate
Using the lubridate package for time spans:
- Interval
- Create an interval using
interval()or%--%- Syntax:
interval(<date/time_object1>, <date/time_object2>)or<date/time_object1> %--% <date/time_object2>
- Syntax:
- Create an interval using
- Periods
- “Periods are time spans but don’t have a fixed length in seconds, instead they work with ‘human’ times, like days and months.” (From R for Data Science)
- Create periods using functions whose name is the time unit pluralized (e.g.,
years(),months(),weeks(),days(),hours(),minutes(),seconds())Example:
days(1)creates a period of 1 day - it does not matter if this day happened to have an extra hour due to daylight savings ending, since periods do not have a physical length## [1] "1d 0H 0M 0S"
- You can add and subtract periods
- You can also use
as.period()to get period of an interval
- Durations
- Durations keep track of the physical amount of time elapsed, so it is “stored as seconds, the only time unit with a consistent length” (From lubridate cheatsheet)
- Create durations using functions whose name is the time unit prefixed with a
d(e.g.,dyears(),dweeks(),ddays(),dhours(),dminutes(),dseconds())Example:
ddays(1)creates a duration of86400s, using the standard conversion of60seconds in an minute,60minutes in an hour, and24hours in a day:## [1] "86400s (~1 days)"Notice that the output says this is equivalent to approximately
1day, since it acknowledges that not all days have24hours. In the case of daylight savings, one particular day may have25hours, so the duration of that day should be represented as:## [1] "90000s (~1.04 days)"
- You can add and subract durations
- You can also use
as.duration()to get duration of an interval
Example: Working with interval
# Use `Sys.timezone()` to get timezone for your location (time is midnight by default)
scorpio_start <- ymd("2019-10-23", tz = Sys.timezone())
scorpio_end <- ymd("2019-11-22", tz = Sys.timezone())
# These datetime objects have class `POSIXct`
class(scorpio_start)## [1] "POSIXct" "POSIXt"# Create interval for the datetimes
scorpio_interval <- scorpio_start %--% scorpio_end # or `interval(scorpio_start, scorpio_end)`
scorpio_interval## [1] 2019-10-23 PDT--2019-11-22 PST## [1] "Interval"
## attr(,"package")
## [1] "lubridate"Example: Working with period
If we use as.period() to get the period of scorpio_interval, we see that it is a period of 30 days. We do not worry about the extra 1 hour gained due to daylight savings ending:
## [1] "30d 0H 0M 0S"## [1] "Period"
## attr(,"package")
## [1] "lubridate"
Because periods work with “human” times like days, it is more intuitive. For example, if we add a period of 30 days to the scorpio_start datetime object, we get the expected end datetime that is 30 days later:
## [1] "2019-10-23 PDT"# After adding 30 day period, we get the expected end datetime (time is midnight)
scorpio_start + days(30)## [1] "2019-11-22 PST"Example: Working with duration
If we use as.duration() to get the duration of scorpio_interval, we see that it is a duration of 2595600 seconds. It takes into account the extra 1 hour gained due to daylight savings ending:
# Duration is 2595600 seconds, which is equivalent to 30 24-hr days + 1 additional hour
scorpio_duration <- as.duration(scorpio_interval)
scorpio_duration## [1] "2595600s (~4.29 weeks)"## [1] "Duration"
## attr(,"package")
## [1] "lubridate"# Using the standard 60s/min, 60min/hr, 24hr/day conversion,
# confirm duration is slightly more than 30 "standard" (ie. 24-hr) days
2595600 / (60 * 60 * 24)## [1] 30.04167# Specifically, it is 30 days + 1 hour, if we define a day to have 24 hours
seconds_to_period(scorpio_duration)## [1] "30d 1H 0M 0S"
Because durations work with physical time, when we add a duration of 30 days to the scorpio_start datetime object, we do not get the end datetime we’d expect:
## [1] "2019-10-23 PDT"# After adding 30 day duration, we do not get the expected end datetime
# `ddays(30)` adds the number of seconds in 30 standard 24-hr days, but one of the days has 25 hours
scorpio_start + ddays(30)## [1] "2019-11-21 23:00:00 PST"# We need to add the additional 1 hour of physical time that elapsed during this time span
scorpio_start + ddays(30) + dhours(1)## [1] "2019-11-22 PST"6 Why use Regular Expressions (Regex)
Credit: Regex Humor (Rex Egg)
In her popular STAT545 class Jenny Bryan, professor of statistics at University of British Columbia, describes regular expressions as:
A God-awful and powerful language for expressing patterns to match in text or for search-and-replace. Frequently described as “write only”, because regular expressions are easier to write than to read/understand. And they are not particularly easy to write.”
Yes, learning regular expressions is painful. So why are we making you do this? Because regular expressions are a fundamental building block of data science
An annoying thing people say is that data science is about trying to find the “signal in the noise”
- Noisy data “is data with a large amount of additional meaningless information in it called noise” Wikipedia
- Prior to data science revolution, quant people thought of “data” as something in columns and rows
- The data science revolution is about creating analysis datasets from many pieces of structured, semi-structured, and unstructured data.
- But processing all this semi-structured data requires a lot of complex (and often tedious) data manipulation.
Another annoying thing people say is that “data science is 80% data cleaning and 20% analysis.”
- Excerpts from a 2014 New York Times article, “For Big-Data Scientists, ‘Janitor Work’ Is Key Hurdle to Insights”:
Much handcrafted work — what data scientists call “data wrangling,” “data munging” and “data janitor work” — is still required. Data scientists, according to interviews and expert estimates, spend from 50 percent to 80 percent of their time mired in this more mundane labor of collecting and preparing unruly digital data, before it can be explored for useful nuggets.
“Data wrangling is a huge — and surprisingly so — part of the job,” said Monica Rogati, vice president for data science at Jawbone, whose sensor-filled wristband and software track activity, sleep and food consumption, and suggest dietary and health tips based on the numbers. “It’s something that is not appreciated by data civilians. At times, it feels like everything we do.”
“It’s an absolute myth that you can send an algorithm over raw data and have insights pop up,” said Jeffrey Heer, a professor of computer science at the University of Washington and a co-founder of Trifacta, a start-up based in San Francisco.
But if the value [of data science] comes from combining different data sets, so does the headache. Data from sensors, documents, the web and conventional databases all come in different formats. Before a software algorithm can go looking for answers, the data must be cleaned up and converted into a unified form that the algorithm can understand.
“Practically, because of the diversity of data, you spend a lot of your time being a data janitor, before you can get to the cool, sexy things that got you into the field in the first place,” said Matt Mohebbi, a data scientist and co-founder of Iodine.
So why learn regular expressions? Because regular expressions are THE preeminent tool for identifying data patterns, and cleaning/transforming “noisy” data
- Most programmers I speak to talk about regular expressions as one of the most important tools for a programmer to learn
- One could argue that regular expressions are a fundamental driver of the data science revolution, in that they are what made it possible to format and integrate diverse data sources into analysis datasets (I don’t know if that is true, but it seems reasonable!)
- For example, web-scraping is fundamentally an application of regular expressions. Grabbing data from the internet is usually very easy. The hard part is processing all that html code into something that can be analyzed.
7 What are regular expressions?
What are regular expressions? from Geeks for Geeks
Regular expressions are an efficient way to match different patterns in strings, similar to the [command + f] function you use to find text in a pdf or word document.
Credit: Crystal Han, Ozan Jaquette, & Karina Salazar (Recruiting the Out-Of-State University)
7.1 str_view() and str_view_all()
The str_view() function:
?str_view
# SYNTAX AND DEFAULT VALUES
str_view(string, pattern, match = NA)
str_view_all(string, pattern, match = NA)- Function:
str_viewshows the first match of a regex pattern;str_view_allshows all the matches of a regex pattern. - Arguments:
string: Input vector. Either a character vector, or something coercible to one.pattern: Pattern to look for.- The default interpretation is a regular expression, as described in stringi::stringi-search-regex. Control options with regex().
match: If TRUE, shows only strings that match the pattern. If FALSE, shows only the strings that don’t match the pattern. Otherwise (the default, NA) displays both matches and non-matches.
str_view will show us the first regex pattern match
Notice how we can see all the regex pattern matches with str_view_all
Example:
str_view & str_view_all regex for newline
Example:
str_view & str_view_all regex for period
Example:
str_view & str_view_all regex for white space
7.2 Escape special character backslashes
If \ is used as an escape character in regular expressions, how do you match a literal \? Well you need to escape it, creating the regular expression \\. To create that regular expression, you need to use a string, which also needs to escape \ . That means to match a literal \ you need to write “\\\\” — you need four backslashes to match one!
Credit: R for Data Science Strings Chapter
The character vector below has one, two, three, and four backslashes.
- Notice once we print this vector, the single backslash returns an empty string and the three backslashes return two backslashes.
## [1] " " "\\" "\\ " "\\\\"- Using
writeLines()we can see view the contents of the strings.
##
## \
## \
## \\8 Regular expression characters
Some common regular expression patterns include (not inclusive):
- Character classes
- Quantifiers
- Anchors
- Groups and ranges
- Backreferences
Credit: DaveChild Regular Expression Cheat Sheet
Select each tab
8.1 Character classes
| STRING (type string that represents regex) |
REGEX (to have this appear in your regex) |
MATCHES (to match with this text) |
|---|---|---|
\\' |
\' |
’ (single quote) |
\\" |
\" |
" (double quote) |
\\\\ |
\\ |
\\ |
\\n |
\n |
new line (return) |
\\t |
\t |
tab |
\\s |
\s |
any whitespace |
\\S |
\S |
any non-whitespace |
\\d |
\d |
any digit |
\\D |
\D |
any non-digit |
\\w |
\w |
any word character |
\\W |
\W |
any non-word character |
\\b |
\b |
word-boundary |
\\B |
\B |
non-word-boundary |
\\. |
\. |
. |
\\! |
\! |
! |
\\? |
\? |
? |
\\( |
\( |
( |
\\) |
\) |
) |
\\{ |
\{ |
{ |
\\} |
\} |
} |
Credit: Working with strings in stringr Cheat sheet
Character classes and special characters in regular expressions
There are certain characters in regex that have special meaning. If you want to search for a digit (number) you need to escape the letter d with a backslash, like \d. The escaped character now can be interpreted as a regular expression. “But wait … there’s more! Before a regex is interpreted as a regular expression, it is also interpreted by R as a string. And backslash is used to escape there as well. So, in the end, you need to preprend two backslashes in order to match a [digit] in a regex.”
Credit: Escaping sequences from Stat 545
## Meet Luke! “No matter where you’re from, @UCBerkeley is a place that will take you out of your comfort zone and shape you into your best self” #IamBerkeley
##
## Here’s Luke on his first day at Berkeley in his dorm, posing with the axe after our big football game win and present day! https://t.co/2fO2hRnmPbLet’s search for instances of the letter “e” in a sentence followed by a space \\s.
Now let’s search for literal exclamation marks \\!
Example: non-word character
\\W
- Using the string vector from above
p12_df$text[39], let’s search for non-word characters.
8.2 Quantifiers
| Character | Description | Code | Result |
|---|---|---|---|
| * | 0 or more | {3} | Exactly 3 |
| + | 1 or more | {3,} | 3 or more |
| ? | 0 or 1 | {3,5} | 3, 4 or 5 |
| \\ | Escape character | \\s | white space |
We use quantifiers to specify the number of times we want to search for a particular pattern.
## Curious as to what your next steps are after being admitted to @UCBerkeley? Join us alongside New Student Services to learn more about what you should be considering as you make your decision & officially become a #BerkeleyBound student!
##
## 🕑 2pm today
## 💻 https://t.co/YukY37REydIn the str_view_all function below we use the + to search for a pattern one or more times. Say we want to search for instances of the letters “ou” one or more times.
Now say we wanted to search for the letter t exactly 2 times in the string.
Example: asterisk
*
- Using the string vector from above
p12_df$text[32], let’s search for instances of “le” zero or more times.
8.3 Anchors
| Character | Description |
|---|---|
| ^ | Start of string, or start of line in multi-line pattern |
| $ | End of string, or end of line in multi-line pattern |
| \b | Word boundary |
| \B | Not word boundary |
## In response to the overwhelming need for hand sanitizer to help combat the #COVID19 pandemic, #WSU is now brewing its own #FDA-approved “Cougar Clean”. #WSUTogether #GoCougs https://t.co/HUoBPydU8F
## The lab experience continues…just in a different form. @CASatWSU instructor Anya Rasmussen, Ph.D., sent mini electricity lab kits to the students in her Physics 150 class. They are using them to construct electromagnets in Zoom breakout rooms. #CougsContain #GoCougs https://t.co/po72Cgk816
## This pandemic can can take away clinical experiences but it can’t take away compassion and care. First-semester @WSUNursing students explain to @WSU_Cougar_Pres how they are making a difference with ☎ outreach. #WSUTogether #WSU #GoCougs
##
## Story ➡ https://t.co/dSl1hcJqdM https://t.co/gb8pxEoHYOLet’s search for the first letter of a string that starts with the letter “T”. We can use the caret symbol ^ to search for the start of the string. Next, we want to search for the letter “T”.
We could use the \\b word bound character followed by the letter “f” to search for a word that starts with the letter “f”.
Example: @ handles
- Using the string vector from above
p12_df$text[20:22], search for Twitter handles.
8.4 Groups and ranges
| Character | Description |
|---|---|
| . | Any character except new line (\n) |
| (a|b) | a or b |
| (…) | Group |
| [abc] | Range (a or b or c) |
| [^abc] | Not (a or b or c) |
| [a-z] | Lower case letter from a to z |
| [A-Z] | Upper case letter from A to Z |
| [0-7] | Digit from 0 to 7 |
We use grouping characters to specify a range of characters.
## Tomorrow, our @WSUEsports Team is facing off against
## @Esports_WA and @SJSU as part of the Electronic Gaming Federation's (@officialEGF) Power Series virtual tournament!
## Tune into the action live at 5:20 PM (UW) and 6 PM (SJSU) PT tomorrow: https://t.co/tzOjeTMaSU
## #GoCougs! https://t.co/5u8EDGaiFHSay we wanted to search for the letter a or o.
What about vowels? We use the square brackets to indicate a range.
If we do not want any vowels we could add the caret ^ symbol to our pattern from above.
Example: Upper case letters
[A-Z]
- Using the string vector from above
p12_df$text[10], let’s search for upper case letters.
8.5 Backreferences
| Character | Description |
|---|---|
| \\1 | Part of the string matched by capturing group 1 |
| \\2 | Part of the string matched by capturing group 2 |
| … | … |
In the previous section we talked about groups and ranges. A parentheses creates what is called a numbered capturing group. “A capturing group stores the part of the string matched by the part of the regular expression inside the parentheses”. For example, if we have one parentheses (a) we can refer to the same text as previously matched by this capturing group with backreferences, like \\1.
Credit: Hadley Wickham (R for Data Science) Grouping and backreferences
## Once again, congratulations to the transfer class of 2022! Please check out our link tree on our bio for more information, and check out our website as well. We are here to help you get started 😎 Woohoo! @ UC… https://t.co/JrcjzGQhOBOur capturing group (what is in the first and only parenthesis) has the letter f. In the first pattern, we are searching for any f's in the text. When we add the backreference \\1 we are now searching for the text matched by our capturing group. In other words, we are searching for ff.
Below we are searching for r or f. When we add the backreference \\1 we are now searching for the text matched by our capturing group. In other words, we are searching for rr or ff.
9 Regex with stringr functions
Using regex in stringr functions (From R for Data Science)
When we specify a pattern in a
stringrfunction, such asstr_view(), it is automatically wrapped in a call toregex()(ie. treated as a regular expression)For simplicity, we can omit the call to
regex()
But, there are additional arguments we can supply to
regex()if we wantedregex(pattern, ignore_case = FALSE, multiline = FALSE, comments = FALSE, ...)
ignore_case: IfTRUE, allows characters to match either their uppercase or lowercase forms
multiline: IfTRUE, allows^and$to match the start and end of each line rather than the start and end of the complete string
comments: IfTRUE, allows you to use comments and white space to make complex regular expressions more understandable- Spaces are ignored, as is everything after
#
- To match a literal space, you’ll need to escape it:
"\\ "
- Spaces are ignored, as is everything after
Example: Specifying
ignore_case = TRUE in regex()
Let’s say we have the following string:
## [1] "Yay, yay.... YAY!"
We can match all the yay’s using the following regex:
Equivalently, we can specify ignore_case = TRUE to avoid dealing with casing variations:
9.1 str_detect()
The str_detect() function:
- Function: Detects the presence or absence of a pattern in a string
- Returns logical vector (
TRUEif there is a match,FALSEif there is not)
- Returns logical vector (
- Arguments:
string: Character vector (or vector coercible to character) to searchpattern: Pattern to look fornegate: If set toTRUE, the returned logical vector will containTRUEif there is not a match andFALSEif there is one
Example: Using
str_detect() on string
# Detects if there is a digit in the string
str_detect(string = "P. Sherman 42 Wallaby Way", pattern = "\\d")## [1] TRUEExample: Using
str_detect() on character vector
# Detects if there is a digit in each string in the vector
str_detect(string = c("One", "25th", "3000"), pattern = "\\d")## [1] FALSE TRUE TRUEExample: Using
str_detect() on dataframe column
Let’s create new columns in p12_df called is_am and is_pm that indicates whether or not each tweet’s created_at time is in the AM or PM, respectively:
p12_df %>%
mutate(
# Returns `TRUE` if the hour is 0#, 10, or 11, `FALSE` otherwise
is_am = str_detect(string = created_at, pattern = " 0\\d| 1[01]"),
# Recall we can set the `negate` argument to switch the returned `TRUE`/`FALSE`
is_pm = str_detect(string = created_at, pattern = " 0\\d| 1[01]", negate = TRUE)
) %>% select(created_at, is_am, is_pm)## # A tibble: 328 x 3
## created_at is_am is_pm
## <dttm> <lgl> <lgl>
## 1 2020-04-25 22:37:18 FALSE TRUE
## 2 2020-04-23 21:11:49 FALSE TRUE
## 3 2020-04-21 04:00:00 TRUE FALSE
## 4 2020-04-24 03:00:00 TRUE FALSE
## 5 2020-04-20 19:00:21 FALSE TRUE
## 6 2020-04-20 02:20:01 TRUE FALSE
## 7 2020-04-22 04:00:00 TRUE FALSE
## 8 2020-04-25 17:00:00 FALSE TRUE
## 9 2020-04-21 15:13:06 FALSE TRUE
## 10 2020-04-21 17:52:47 FALSE TRUE
## # … with 318 more rows
Because TRUE evaluates to 1 and FALSE evaluates to 0 in a numerical context, we could also sum the returned logical vector to see how many of the elements in the vector had a match:
# Number of tweets that were created in the AM
num_am_tweets <- sum(str_detect(string = p12_df$created_at, pattern = " 0\\d| 1[01]"))
num_am_tweets## [1] 53
Additionally, we can take the average of the logical vector to get the proportion of elements in the input vector that had a match:
# Proportion of tweets that were created in the AM
pct_am_tweets <- mean(str_detect(string = p12_df$created_at, pattern = " 0\\d| 1[01]"))
pct_am_tweets## [1] 0.1615854
We can also use the logical vector returned from str_detect() to filter p12_df to only include rows that had a match:
# Keep only rows whose tweet was created in the AM
p12_df %>%
filter(str_detect(string = created_at, pattern = " 0\\d| 1[01]"))## # A tibble: 53 x 5
## user_id created_at screen_name text location
## <chr> <dttm> <chr> <chr> <chr>
## 1 22080148 2020-04-21 04:00:00 WSUPullman "Darien McLaughlin… Pullman, W…
## 2 22080148 2020-04-24 03:00:00 WSUPullman 6 houses, one pick… Pullman, W…
## 3 22080148 2020-04-20 02:20:01 WSUPullman Tell us one of you… Pullman, W…
## 4 22080148 2020-04-22 04:00:00 WSUPullman We loved seeing yo… Pullman, W…
## 5 22080148 2020-04-24 01:58:04 WSUPullman #WSU agricultural … Pullman, W…
## 6 22080148 2020-04-22 02:22:03 WSUPullman Nice 👍 https://t.c… Pullman, W…
## 7 15988549 2020-04-20 02:52:31 CalAdmissi… @PaulineARoxas Con… Berkeley, …
## 8 15988549 2020-04-22 03:07:00 CalAdmissi… It’s time to make … Berkeley, …
## 9 15988549 2020-04-22 00:00:08 CalAdmissi… "Are you a #Berkel… Berkeley, …
## 10 15988549 2020-04-20 03:03:21 CalAdmissi… "@N48260756 We sug… Berkeley, …
## # … with 43 more rows9.2 str_subset()
The str_subset() function:
- Function: Keeps strings that match a pattern
- Returns input vector filtered to only keep elements that match the specified pattern
- Arguments:
string: Character vector (or vector coercible to character) to searchpattern: Pattern to look fornegate: If set toTRUE, the returned vector will contain only elements that did not match the specified pattern
Example: Using
str_subset() on character vector
# Subsets the input vector to only keep elements that contain a digit
str_subset(string = c("One", "25th", "3000"), pattern = "\\d")## [1] "25th" "3000"Example: Using
str_subset() on dataframe column
# Subsets the `created_at` vector of `p12_df` to only keep elements that occured in the AM
str_subset(string = p12_df$created_at, pattern = " 0\\d| 1[01]")## [1] "2020-04-21 04:00:00" "2020-04-24 03:00:00" "2020-04-20 02:20:01"
## [4] "2020-04-22 04:00:00" "2020-04-24 01:58:04" "2020-04-22 02:22:03"
## [7] "2020-04-20 02:52:31" "2020-04-22 03:07:00" "2020-04-22 00:00:08"
## [10] "2020-04-20 03:03:21" "2020-04-22 00:47:00" "2020-04-23 06:34:00"
## [13] "2020-04-23 04:06:49" "2020-04-19 03:32:21" "2020-04-20 02:53:38"
## [16] "2020-04-20 02:53:14" "2020-04-20 03:04:11" "2020-04-19 03:30:14"
## [19] "2020-04-20 02:58:55" "2020-04-19 05:37:00" "2020-04-21 02:34:00"
## [22] "2020-04-20 00:15:07" "2020-04-25 04:18:29" "2020-04-25 00:00:01"
## [25] "2020-04-21 02:33:00" "2020-04-24 01:00:01" "2020-04-23 02:38:46"
## [28] "2020-04-24 04:48:28" "2020-04-24 01:06:33" "2020-04-25 04:48:08"
## [31] "2020-04-22 00:10:43" "2020-04-21 05:58:12" "2020-04-24 01:41:19"
## [34] "2020-04-24 01:42:44" "2020-04-24 01:43:11" "2020-04-23 02:45:24"
## [37] "2020-04-20 00:44:42" "2020-04-24 01:41:13" "2020-04-25 00:26:02"
## [40] "2020-04-25 00:31:23" "2020-04-25 00:46:40" "2020-04-25 00:20:36"
## [43] "2020-04-20 00:09:58" "2020-04-20 00:09:46" "2020-04-20 00:10:08"
## [46] "2020-04-25 00:29:12" "2020-04-22 01:45:02" "2020-04-23 02:00:14"
## [49] "2020-04-25 00:34:47" "2020-04-24 02:11:51" "2020-04-25 00:05:59"
## [52] "2020-04-21 04:14:11" "2020-04-23 02:13:21"9.3 str_extract() and str_extract_all()
The str_extract() and str_extract_all() functions:
?str_extract
# SYNTAX
str_extract(string, pattern)
?str_extract_all
# SYNTAX AND DEFAULT VALUES
str_extract_all(string, pattern, simplify = FALSE)- Function: Extracts matching patterns from a string
- Returns first match (
str_extract()) or all matches (str_extract_all()) for input vector
- Returns first match (
- Arguments:
string: Character vector (or vector coercible to character) to searchpattern: Pattern to look forsimplify: If set toTRUE, the returned matches will be in a character matrix rather than the default list of character vectors
Example: Using
str_extract() and str_extract_all() on character vector
[str_extract()] Extract the first occurrence of a word for each string:
# Extracts first match of a word
str_extract(string = c("Three French hens", "Two turtle doves", "A partridge in a pear tree"),
pattern = "\\w+")## [1] "Three" "Two" "A"[str_extract_all()] Extract all occurrences of a word for each string:
# Extracts all matches of a word, returning a list of character vectors
str_extract_all(string = c("Three French hens", "Two turtle doves", "A partridge in a pear tree"),
pattern = "\\w+")## [[1]]
## [1] "Three" "French" "hens"
##
## [[2]]
## [1] "Two" "turtle" "doves"
##
## [[3]]
## [1] "A" "partridge" "in" "a" "pear" "tree"# Extracts all matches of a word, returning a character matrix
str_extract_all(string = c("Three French hens", "Two turtle doves", "A partridge in a pear tree"),
pattern = "\\w+", simplify = TRUE)## [,1] [,2] [,3] [,4] [,5] [,6]
## [1,] "Three" "French" "hens" "" "" ""
## [2,] "Two" "turtle" "doves" "" "" ""
## [3,] "A" "partridge" "in" "a" "pear" "tree"Example: Using
str_extract() and str_extract_all() on dataframe column
[str_extract()] Extract first hashtag:
# Extracts first match of a hashtag (if there is one)
p12_df %>%
mutate(
hashtag = str_extract(string = text, pattern = "#\\S+")
) %>% select(text, hashtag)## # A tibble: 328 x 2
## text hashtag
## <chr> <chr>
## 1 "Big Dez is headed to Indy!\n\n#GoCougs | #NFLDraft2020 | @dad… #GoCougs
## 2 Cougar Cheese. That's it. That's the tweet. 🧀#WSU #GoCougs htt… #WSU
## 3 "Darien McLaughlin '19, and her dog, Yuki, went on a #Pullman … #Pullman
## 4 6 houses, one pick. Cougs, which one you got? Reply ⬇️ #WSU #… #WSU
## 5 Why did you choose to attend @WSUPullman?🤔 #WSU #GoCougs https… #WSU
## 6 Tell us one of your Bryan Clock Tower memories ⏰ 🐾 #WSU #GoCou… #WSU
## 7 We loved seeing your top three @WSUPullman buildings, but what… #WSU
## 8 "Congratulations, graduates! We’re two weeks away from the #WS… #WSU
## 9 Learn more about this story at https://t.co/45BzKc2rFE. #WSU #… #WSU
## 10 "Tomorrow, our @WSUEsports Team is facing off against \n@Espor… #GoCoug…
## # … with 318 more rows[str_extract_all()] Extract all hashtags:
# Extracts all matches of hashtags (if there are any)
p12_df %>%
mutate(
hashtag_vector = str_extract_all(string = text, pattern = "#\\S+"),
# Use `as.character()` so we can see the content of the character vector of matches
hashtags = as.character(hashtag_vector)
) %>% select(text, hashtag_vector, hashtags)## # A tibble: 328 x 3
## text hashtag_vector hashtags
## <chr> <list> <chr>
## 1 "Big Dez is headed to Indy!\n\n… <chr [3]> "c(\"#GoCougs\", \"#NFL…
## 2 Cougar Cheese. That's it. That'… <chr [2]> "c(\"#WSU\", \"#GoCougs…
## 3 "Darien McLaughlin '19, and her… <chr [3]> "c(\"#Pullman\", \"#Cou…
## 4 6 houses, one pick. Cougs, whic… <chr [3]> "c(\"#WSU\", \"#CougsCo…
## 5 Why did you choose to attend @W… <chr [2]> "c(\"#WSU\", \"#GoCougs…
## 6 Tell us one of your Bryan Clock… <chr [2]> "c(\"#WSU\", \"#GoCougs…
## 7 We loved seeing your top three … <chr [2]> "c(\"#WSU\", \"#GoCougs…
## 8 "Congratulations, graduates! We… <chr [3]> "c(\"#WSU\", \"#CougGra…
## 9 Learn more about this story at … <chr [2]> "c(\"#WSU\", \"#GoCougs…
## 10 "Tomorrow, our @WSUEsports Team… <chr [1]> #GoCougs!
## # … with 318 more rows9.4 str_match() and str_match_all()
The str_match() and str_match_all() functions:
?str_match
# SYNTAX
str_match(string, pattern)
?str_match_all
# SYNTAX
str_match_all(string, pattern)- Function: Extracts matched groups from a string
- Returns a character matrix containing the full match in the first column, then additional columns for matches from each capturing group
- Arguments:
string: Character vector (or vector coercible to character) to searchpattern: Pattern to look for
Example: Using
str_match() and str_match_all() on character vector
[str_match()] Extract the first month, day, year for each string:
# Extracts first match of month, day, year
str_match(string = c("5-1-2020", "12/25/17", "01.01.13 to 01.01.14"),
pattern = "(\\d+)[-/\\.](\\d+)[-/\\.](\\d+)")## [,1] [,2] [,3] [,4]
## [1,] "5-1-2020" "5" "1" "2020"
## [2,] "12/25/17" "12" "25" "17"
## [3,] "01.01.13" "01" "01" "13"[str_match_all()] Extract all month, day, year for each string:
# Extracts all matches of month, day, year
str_match_all(string = c("5-1-2020", "12/25/17", "01.01.13 to 01.01.14"),
pattern = "(\\d+)[-/\\.](\\d+)[-/\\.](\\d+)")## [[1]]
## [,1] [,2] [,3] [,4]
## [1,] "5-1-2020" "5" "1" "2020"
##
## [[2]]
## [,1] [,2] [,3] [,4]
## [1,] "12/25/17" "12" "25" "17"
##
## [[3]]
## [,1] [,2] [,3] [,4]
## [1,] "01.01.13" "01" "01" "13"
## [2,] "01.01.14" "01" "01" "14"Example: Using
str_match() on dataframe column
datetime_regex <- "([\\d-]+) ([\\d:]+)"
p12_df %>%
mutate(
# The 1st capturing group will be in the 2nd column of the matrix returned from `str_match()`
date = str_match(string = created_at, pattern = datetime_regex)[, 2],
# The 2nd capturing group will be in the 3rd column of the matrix returned from `str_match()`
time = str_match(string = created_at, pattern = datetime_regex)[, 3]
) %>% select(created_at, date, time)## # A tibble: 328 x 3
## created_at date time
## <dttm> <chr> <chr>
## 1 2020-04-25 22:37:18 2020-04-25 22:37:18
## 2 2020-04-23 21:11:49 2020-04-23 21:11:49
## 3 2020-04-21 04:00:00 2020-04-21 04:00:00
## 4 2020-04-24 03:00:00 2020-04-24 03:00:00
## 5 2020-04-20 19:00:21 2020-04-20 19:00:21
## 6 2020-04-20 02:20:01 2020-04-20 02:20:01
## 7 2020-04-22 04:00:00 2020-04-22 04:00:00
## 8 2020-04-25 17:00:00 2020-04-25 17:00:00
## 9 2020-04-21 15:13:06 2020-04-21 15:13:06
## 10 2020-04-21 17:52:47 2020-04-21 17:52:47
## # … with 318 more rows9.5 str_replace() and str_replace_all()
The str_replace() and str_replace_all() functions:
?str_replace
# SYNTAX
str_replace(string, pattern, replacement)
?str_replace_all
# SYNTAX
str_replace_all(string, pattern, replacement)- Function: Replaces matched patterns in a string
- Returns input vector with first match (
str_replace()) or all matches (str_replace_all()) for each string replaced with specified replacement
- Returns input vector with first match (
- Arguments:
string: Character vector (or vector coercible to character) to searchpattern: Pattern to look forreplacement: What the matched pattern should be replaced with
str_replace_all()also supports multiple replacements, where you can omit thereplacementargument and just provide a named vector of replacements as thepattern
Example: Using
str_replace() and str_replace_all()
[str_replace()] Replace the first occurrence of a vowel:
# Replace first vowel with empty string
str_replace(string = "Thanks for the Memories", pattern = "[aeiou]", replacement = "")## [1] "Thnks for the Memories"[str_replace_all()] Replace all occurrences of a vowel:
# Replace all vowels with empty strings
str_replace_all(string = "Thanks for the Memories", pattern = "[aeiou]", replacement = "")## [1] "Thnks fr th Mmrs"Example: Using backreferences with
str_replace() and str_replace_all()
[str_replace()] Reorders the first date that is matched:
# Use \\1, \\2, and \\3 to refer to the capturing groups (ie. month, day, year)
str_replace(string = "12/31/19 to 01/01/20", pattern = "(\\d+)/(\\d+)/(\\d+)",
replacement = "20\\3-\\1-\\2")## [1] "2019-12-31 to 01/01/20"[str_replace_all()] Reorders all dates that are matched:
# Use \\1, \\2, and \\3 to refer to the capturing groups (ie. month, day, year)
str_replace_all(string = "12/31/19 to 01/01/20", pattern = "(\\d+)/(\\d+)/(\\d+)",
replacement = "20\\3-\\1-\\2")## [1] "2019-12-31 to 2020-01-01"Example: Using
str_replace_all() for multiple replacements
# Replace all occurrences of "at" with "@", and all digits with "#"
str_replace_all(string = "Tomorrow at 10:30AM", pattern = c("at" = "@", "\\d" = "#"))## [1] "Tomorrow @ ##:##AM"Example: Using
str_replace_all() on dataframe column
p12_df %>%
mutate(
# Replace all hashtags and handles from tweet with an empty string
removed_hashtags_handles = str_replace_all(string = text, pattern = "[@#]\\S+", replacement = "")
) %>% select(text, removed_hashtags_handles)## # A tibble: 328 x 2
## text removed_hashtags_handles
## <chr> <chr>
## 1 "Big Dez is headed to Indy!\n\n#… "Big Dez is headed to Indy!\n\n | | …
## 2 Cougar Cheese. That's it. That's… Cougar Cheese. That's it. That's the …
## 3 "Darien McLaughlin '19, and her … "Darien McLaughlin '19, and her dog, …
## 4 6 houses, one pick. Cougs, which… 6 houses, one pick. Cougs, which one …
## 5 Why did you choose to attend @WS… Why did you choose to attend https…
## 6 Tell us one of your Bryan Clock … Tell us one of your Bryan Clock Tower…
## 7 We loved seeing your top three @… We loved seeing your top three build…
## 8 "Congratulations, graduates! We’… "Congratulations, graduates! We’re tw…
## 9 Learn more about this story at h… "Learn more about this story at https…
## 10 "Tomorrow, our @WSUEsports Team … "Tomorrow, our Team is facing off ag…
## # … with 318 more rows9.6 str_split()
The str_split() function:
- Function: Splits a string by specified pattern
- Returns character vector containing the split substrings
- Arguments:
string: Character vector (or vector coercible to character) to searchpattern: Pattern to look for and split byn: Maximum number of substrings to returnsimplify: If set toTRUE, the returned matches will be in a character matrix rather than the default list of character vectors
Example: Using
str_split() on character vector
# Split by comma or the word "and"
str_split(string = c("The Lion, the Witch, and the Wardrobe", "Peanut butter and jelly"),
pattern = ",? and |, ")## [[1]]
## [1] "The Lion" "the Witch" "the Wardrobe"
##
## [[2]]
## [1] "Peanut butter" "jelly"
We can specify n to control the maximum number of substrings we want to return:
# Limit split to only return 2 substrings
str_split(string = c("The Lion, the Witch, and the Wardrobe", "Peanut butter and jelly"),
pattern = ",? and |, ", n = 2)## [[1]]
## [1] "The Lion" "the Witch, and the Wardrobe"
##
## [[2]]
## [1] "Peanut butter" "jelly"
We can specify simplify = TRUE to return a character matrix instead of a list:
# Return split substrings in a character matrix
str_split(string = c("The Lion, the Witch, and the Wardrobe", "Peanut butter and jelly"),
pattern = ",? and |, ", simplify = TRUE)## [,1] [,2] [,3]
## [1,] "The Lion" "the Witch" "the Wardrobe"
## [2,] "Peanut butter" "jelly" ""Example: Using
str_split() on dataframe column
When we split the created_at field at either a hyphen or space, we can separated out the year, month, day, and time components of the string:
p12_df %>%
mutate(
# Use `as.character()` so we can see the content of the character vector of splitted strings
year_month_day_time = as.character(str_split(string = created_at, pattern = "[- ]"))
) %>% select(created_at, year_month_day_time)## # A tibble: 328 x 2
## created_at year_month_day_time
## <dttm> <chr>
## 1 2020-04-25 22:37:18 "c(\"2020\", \"04\", \"25\", \"22:37:18\")"
## 2 2020-04-23 21:11:49 "c(\"2020\", \"04\", \"23\", \"21:11:49\")"
## 3 2020-04-21 04:00:00 "c(\"2020\", \"04\", \"21\", \"04:00:00\")"
## 4 2020-04-24 03:00:00 "c(\"2020\", \"04\", \"24\", \"03:00:00\")"
## 5 2020-04-20 19:00:21 "c(\"2020\", \"04\", \"20\", \"19:00:21\")"
## 6 2020-04-20 02:20:01 "c(\"2020\", \"04\", \"20\", \"02:20:01\")"
## 7 2020-04-22 04:00:00 "c(\"2020\", \"04\", \"22\", \"04:00:00\")"
## 8 2020-04-25 17:00:00 "c(\"2020\", \"04\", \"25\", \"17:00:00\")"
## 9 2020-04-21 15:13:06 "c(\"2020\", \"04\", \"21\", \"15:13:06\")"
## 10 2020-04-21 17:52:47 "c(\"2020\", \"04\", \"21\", \"17:52:47\")"
## # … with 318 more rows9.7 str_count()
The str_count() function:
- Function: Counts the number of matches in a string
- Returns the number of matches
- Arguments:
string: Character vector (or vector coercible to character) to searchpattern: Pattern to look for
Example: Using
str_count() on character vector
# Counts the number of digits
str_count(string = c("H2O2", "Year 3000", "4th of July"), pattern = "\\d")## [1] 2 4 1Example: Using
str_count() on dataframe column
p12_df %>%
mutate(
# Counts the total number of hashtags and mentions
num_hashtags_and_mentions = str_count(string = text, pattern = "[@#]\\S+")
) %>% select(text, num_hashtags_and_mentions)## # A tibble: 328 x 2
## text num_hashtags_and_men…
## <chr> <int>
## 1 "Big Dez is headed to Indy!\n\n#GoCougs | #NFLDra… 5
## 2 Cougar Cheese. That's it. That's the tweet. 🧀#WSU… 2
## 3 "Darien McLaughlin '19, and her dog, Yuki, went o… 4
## 4 6 houses, one pick. Cougs, which one you got? Rep… 3
## 5 Why did you choose to attend @WSUPullman?🤔 #WSU #… 3
## 6 Tell us one of your Bryan Clock Tower memories ⏰ … 2
## 7 We loved seeing your top three @WSUPullman buildi… 3
## 8 "Congratulations, graduates! We’re two weeks away… 3
## 9 Learn more about this story at https://t.co/45BzK… 2
## 10 "Tomorrow, our @WSUEsports Team is facing off aga… 5
## # … with 318 more rows9.8 str_locate() and str_locate_all()
The str_locate() and str_locate_all() functions:
?str_locate
# SYNTAX
str_locate(string, pattern)
?str_locate_all
# SYNTAX
str_locate_all(string, pattern)- Function: Locates the position of patterns in a string
- Returns an integer matrix containing the start position of match in the first column and end position of match in second column
- Arguments:
string: Character vector (or vector coercible to character) to searchpattern: Pattern to look for
Example: Using
str_locate() and str_locate_all() on character vector
[str_locate()] Locate the start and end positions for first stretch of numbers:
# Locate positions for first stretch of numbers
str_locate(string = c("555.123.4567", "(555) 135-7900 and (555) 246-8000"),
pattern = "\\d+")## start end
## [1,] 1 3
## [2,] 2 4[str_locate_all()] Locate the start and end positions for all stretches of numbers:
# Locate positions for all stretches of numbers
str_locate_all(string = c("555.123.4567", "(555) 135-7900 and (555) 246-8000"),
pattern = "\\d+")## [[1]]
## start end
## [1,] 1 3
## [2,] 5 7
## [3,] 9 12
##
## [[2]]
## start end
## [1,] 2 4
## [2,] 7 9
## [3,] 11 14
## [4,] 21 23
## [5,] 26 28
## [6,] 30 33Example: Using
str_locate() on dataframe column
p12_df %>%
mutate(
# Start position of first hashtag in tweet (ie. 1st column of matrix returned from `str_locate()`)
start_of_first_hashtag = str_locate(string = text, pattern = "#\\S+")[, 1],
# End position of first hashtag in tweet (ie. 2nd column of matrix returned from `str_locate()`)
end_of_first_hashtag = str_locate(string = text, pattern = "#\\S+")[, 2],
# Length of first hashtag in tweet (ie. difference between start and end positions)
length_of_first_hashtag = end_of_first_hashtag - start_of_first_hashtag
) %>% select(text, start_of_first_hashtag, end_of_first_hashtag, length_of_first_hashtag)## # A tibble: 328 x 4
## text start_of_first_ha… end_of_first_ha… length_of_first_…
## <chr> <int> <int> <int>
## 1 "Big Dez is heade… 29 36 7
## 2 Cougar Cheese. Th… 46 49 3
## 3 "Darien McLaughli… 53 60 7
## 4 6 houses, one pic… 57 60 3
## 5 Why did you choos… 44 47 3
## 6 Tell us one of yo… 52 55 3
## 7 We loved seeing y… 144 147 3
## 8 "Congratulations,… 59 62 3
## 9 Learn more about … 57 60 3
## 10 "Tomorrow, our @W… 266 274 8
## # … with 318 more rows10 HTML
Markup Language
“A markup language is a computer language that uses tags to define elements within a document. It is human-readable, meaning markup files contain standard words, rather than typical programming syntax.”
Credit: Markup Language from TechTerms
Hypertext Markup Language (HTML)
- HTML is a markup language for the creation of websites
- HTML puts the content on the webpage, but does not “style” the page (e.g., fonts, colors, background)
- CSS (Cascading Style Sheets) adds style to the webpage (e.g., fonts, colors, etc.)
- Javascript adds functionality to the webpage
10.1 HTML Basics
Intro to HTML (and CSS)
- Watch this excellent 12-minute introductory HTML tutorial by LearnCode.academy
- Watch this 7-minute introductory CSS tutorial by LearnCode.academy
A Simple HTML Document (From w3schools)
- HTML consists of a series of elements
- Elements are defined by a start tag, some content, and an end tag:
<tagname> Content </tagname>
- Elements can be nested within one another
- Elements are defined by a start tag, some content, and an end tag:
- Components of a basic HTML document:
- Begin with
<!DOCTYPE html>to indicate it is an HTML document - The
<html>element is the root element of an HTML page, where all other elements are nested - The
<head>element contains meta information about the document (ie. not displayed on webpage)- Including CSS style to apply to html content
- The
<body>element contains the visible page content
- Begin with
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<h1>My First Heading</h1>
<p>My first paragraph.</p>
</body>
</html>10.3 Attributes
What are attributes?
- Attributed in HTML elements are optional, but all HTML elements can have attributes
- Attributes are used to specify additional characteristics of elements
- Attributes are always specified in the start tag
- Attributes usually come in name/value pairs like:
name="value"
Credit: HTML attributes from W3schools
Some common attributes you may encounter:
The
hrefattribute for an<a>tag (specifies url to link to):<a href="https://www.w3schools.com">This is a link</a>The
srcattribute for an<img>tag (specifies image to display):<img src="html_cheatsheet.jpg">You can add more than one attribute to an element:
<img src="html_cheatsheet.jpg" width="200" height="300">The
classandidattributes are also commonly added to elements to be able to identify and select for them
10.3.1 class
- The
classattribute can specify one or more class names for an HTML element - An element can be identified by its class
- You can select for an element by its class using
.followed by the class name (more from GeekstoGeeks here)- For example, this can be used in CSS to select for and style all elements with a specific class
HTML:
<div class="countries">
<h3>United States</h3>
<p class="place">Washington D.C.</p>
<img src="https://cdn.aarp.net/content/dam/aarp/travel/destination-guides/2018/03/1140-trv-dst-dc-main.imgcache.revd66f01d4a19adcecdb09fdacd4471fa8.jpg">
</div>
<div class="countries">
<h3>Mexico</h3>
<p class="place">Guadalajara</p>
<img src="https://cityofguadalajara.com/wp-content/uploads/2016/11/Centro-Historico-de-Guadalajara-800x288.jpg">
</div>CSS:
<style>
.countries {
background-color: #e6e6e6;
color: #336699;
margin: 10px;
padding: 15px;
}
.place {
color: black;
}
</style>Result:
United States
Washington D.C
Mexico
Guadalajara
Credit: HTML Classes from W3schools
10.3.2 id
- The
idattribute is used to specify one unique HTML element within the HTML document - An element can be identified by its id
- You can select for an element by its id using
#followed by the id name (more from GeekstoGeeks here)- For example, this can be used in CSS to select for and style a specific element with a certain id
HTML:
CSS:
<style>
#banner {
background-color: #e6e6e6;
font-size: 40px;
padding: 20px;
text-align: center;
}
</style>Result:
Credit: HTML Id from W3schools
10.4 Student Exercise
- Spend 5-10 minutes playing with the simple HTML text below; experiment with whichever additional elements/tags/attributes/etc you want
- Paste the below code into TryIt Editor and click Run
<!DOCTYPE html>
<html>
<head>
<title>Page title (in head tag)</title>
</head>
<body>
<h1>Title of level 1 heading</h1>
<p>My first paragraph.</p>
<p>My second paragraph.</p>
<p>Add some bold text <strong>right here</strong></p>
<p>Add some italics text <em>right here</em></p>
<p>Include a hyperlink tag within a paragraph tag. this book looks interesting : <a href="https://bookdown.org/rdpeng/rprogdatascience/">R Programming for Data Science</a></p>
<p>Include another hyperlink tag within a paragraph tag. chapter on <a href="https://bookdown.org/rdpeng/rprogdatascience/regular-expressions.html">Regular Expressions</a></p>
<p> put a button inside this paragraph <button>I am a button!</button></p>
<p>Here are some items in a list, but items not placed within an unordered list </p>
<li> text you want in item</li>
<li> text you want in another item</li>
<p>Here are some items in an unordered list</p>
<ul>
<li> first item in unordered list </li>
<li> second item in unordered list </li>
</ul>
</body>
</html>10.5 HTML Resources
Lots of wonderful resources on the web to learn HTML!
- Use this website to create/modify HTML code and view the result after it is compiled
- HTML cheat sheets
- Link to HTML cheat sheet (PDF)
- Link to another HTML cheat sheet, (shown below)
11 Web scraping using rvest
The rvest package
rvesthelps you scrape information from web pages. It is designed to work with magrittr to make it easy to express common web scraping tasks, inspired by libraries like beautiful soup.
- Source:
rvestwebpage
[
rvestpackage contains] Wrappers around thexml2andhttrpackages to make it easy to download, then manipulate, HTML and XML.
- Source:
rvestpackage documentation
Why use the rvest package?
rvestmakes it easy to parse HTML- First, we use the
read_html()function to read in the HTML and convert it to anxml_document/xml_nodeobject - A node is just an HTML element
- HTML is made up of nested elements, so once we’ve read in the HTML to a
xml_nodeobject, we can easily traverse the nested nodes (ie. children elements) and parse the HTML rvestcomes with many helpful functions to search and extract various parts of the HTMLhtml_node()/html_nodes(): Search and extract node(s) (ie. HTML elements)html_text(): Extract the content between HTML tagshtml_attr()/html_attrs(): Extract the attribute(s) of HTML tags
11.1 Reading HTML
The read_html() function:
?read_html
# SYNTAX AND DEFAULT VALUES
read_html(x, encoding = "", ..., options = c("RECOVER", "NOERROR", "NOBLANKS"))- Arguments:
x: The input can be a string containing HTML or url to the webpage you want to scrape
- Output:
- The HTML that is read in will be returned as an
rvestxml_document/xml_nodeobject and can be easily parsed - You can also view the raw HTML using
as.character()
- The HTML that is read in will be returned as an
Scraping HTML from a webpage:
- Navigate to the webpage (e.g., https://corona.help/) in your browser
- If possible, use Google Chrome or Mozilla Firefox
- View the HTML of the page by right clicking >
View Page Source- This will be the raw HTML that is scraped when we use
read_html()
- This will be the raw HTML that is scraped when we use
- When you right click, you may notice another option called
Inspect(Chrome) orInspect Element(Firefox) that will pop up a side panel- This can be helpful for visualizing the HTML elements on the page
- You can also click on this side panel and hit
ctrl+f(Windows) orcmd+f(Macs) to search for elements using a selector - But note that the HTML you see here might not be the same as what you see in
View Page Source(i.e., what is scraped), since it also reflects changes made to the HTML after the page was loaded (e.g., by JavaScript)
Example: Using
read_html() to read in HTML from string
## {html_document}
## <html>
## [1] <body>\n<h1>This is a heading.</h1>\n<p>This is a paragraph.</p>\n</ ...## [1] "xml_document" "xml_node"## [1] "<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.0 Transitional//EN\" \"http://www.w3.org/TR/REC-html40/loose.dtd\">\n<html><body>\n<h1>This is a heading.</h1>\n<p>This is a paragraph.</p>\n</body></html>\n"Example: Using
read_html() to scrape the page https://corona.help/
## {html_document}
## <html class="loading" lang="en" data-textdirection="ltr">
## [1] <head>\n<meta http-equiv="Content-Type" content="text/html; charset= ...
## [2] <body class="horizontal-layout horizontal-menu dark-layout 2-columns ...## [1] "xml_document" "xml_node"## chr "<!DOCTYPE html>\n<html class=\"loading\" lang=\"en\" data-textdirection=\"ltr\">\n<!-- BEGIN: Head--><head>\n<m"| __truncated__11.2 Parsing HTML
The html_node() and html_nodes() functions:
- Arguments:
x: Anrvestxml_document/xml_nodeobject (useread_html()to get this)css: Selector (can select by HTML tag name, its attributes, etc.)
- Output:
html_node()returns the first element that it finds as anrvestxml_nodeobject- Recall that a node is just an HTML element
html_nodes()returns all elements that it finds as anrvestxml_nodesetobject- All elements that are selected will be returned in a nodeset
- Again, you can view the raw HTML using
as.character()- Syntax:
as.character(html_node(...))
- Syntax:
Selecting for HTML elements:
- HTML elements can be selected in many ways
- Selecting by tagname:
'p','table', etc. - Selecting by class using
.:'.my-class' - Selecting by id using
#:'#my-id' - Selecting nested elements:
'table tr'(selects all rows within a table)
- Selecting by tagname:
- You can test your selector in your browser
- Right click and select
Inspect(Chrome) orInspect Element(Firefox) to bring up a side panel - Hit
ctrl+f(Windows) orcmd+f(Macs) and enter your selector to search for elements
- Right click and select
Example: Using
html_node() and html_nodes() I
Remember that the input to html_node()/html_nodes() should be an rvest xml_document/xml_node object, which we can obtain from read_html():
html <- read_html("<p>Paragraph #1</p><p>Paragraph #2</p><p>Paragraph #3</p>")
# View class of object
class(html)## [1] "xml_document" "xml_node"## [1] "<!DOCTYPE html PUBLIC \"-//W3C//DTD HTML 4.0 Transitional//EN\" \"http://www.w3.org/TR/REC-html40/loose.dtd\">\n<html><body>\n<p>Paragraph #1</p>\n<p>Paragraph #2</p>\n<p>Paragraph #3</p>\n</body></html>\n"
If we search for the <p> element using html_node(), it will return the first result:
## [1] "xml_node"## [1] "<p>Paragraph #1</p>\n"
If we search for the <p> element using html_nodes(), it will return all results:
## [1] "xml_nodeset"## [1] "<p>Paragraph #1</p>\n" "<p>Paragraph #2</p>\n" "<p>Paragraph #3</p>"
Note that we could also use %>%:
Example: Using
html_node() and html_nodes() II
Let’s revisit the HTML we scraped from https://corona.help/ in the previous example
- We will try selecting for the “Total by country” table off of that page
- In your browser, right click >
View Page Sourceto check that thetableelement is indeed in the scraped HTML - Then, you can right click the table on the page and inspect it to better visualize the elements
## [1] "xml_document" "xml_node"
Select for the <table> element on that page using html_node():
# Since this table is the only table on the page, we can just use `html_node()`
corona_table <- corona %>% html_node('table')
corona_table## {html_node}
## <table class="table table-striped table-hover-animation mb-0" id="table">
## [1] <thead id="thead"><tr>\n<th>COUNTRY</th>\n ...
## [2] <tbody>\n<tr>\n<td><a href="https://corona.help/country/united-state ...## [1] "xml_node"
Select all rows in the table (i.e., <tr> elements) using html_nodes()
- It makes sense to select by row (rather than column) because each row usually represent an observation
- The way HTML tables are structured also makes it easier to extract information by row because each
<tr>element (i.e., row) has<th>/<td>elements (i.e., column cells) nested within it, and not the other way around - But if you wanted to select a certain column, there are ways to do that as well (e.g.,
table tr td:nth-child(1)selects the first cell in each row a.k.a. the first column in table)
# We can chain `html_node()`/`html_nodes()` functions
corona_rows <- corona %>% html_node('table') %>% html_nodes('tr')
# Alternatively, we can use `table tr` as the selector to select all `tr` elements within a `table`
corona_rows <- corona %>% html_nodes('table tr')
# Investigate object
head(corona_rows) # View first few rows## {xml_nodeset (6)}
## [1] <tr>\n<th>COUNTRY</th>\n <th>INFECTED</th>\ ...
## [2] <tr>\n<td><a href="https://corona.help/country/united-states">\n ...
## [3] <tr>\n<td><a href="https://corona.help/country/india">\n ...
## [4] <tr>\n<td><a href="https://corona.help/country/brazil">\n ...
## [5] <tr>\n<td><a href="https://corona.help/country/russia">\n ...
## [6] <tr>\n<td><a href="https://corona.help/country/united-kingdom">\n ...## [1] "list"## [1] "xml_nodeset"## [1] 22611.2.1 Practicing regex
The following examples use the Coronavirus data from https://corona.help/
- Recall that we have selected for all rows in the data table on that page in the previous example
- If we wanted to try and create a dataframe out of this table, we could further select each cell in the table (i.e.,
<td>elements from each row), but this would involve loops which will be covered in a later lecture - For now, we will be practicing parsing data from each row using regex
View corona_rows we selected from previous example:
## {xml_nodeset (6)}
## [1] <tr>\n<th>COUNTRY</th>\n <th>INFECTED</th>\ ...
## [2] <tr>\n<td><a href="https://corona.help/country/united-states">\n ...
## [3] <tr>\n<td><a href="https://corona.help/country/india">\n ...
## [4] <tr>\n<td><a href="https://corona.help/country/brazil">\n ...
## [5] <tr>\n<td><a href="https://corona.help/country/russia">\n ...
## [6] <tr>\n<td><a href="https://corona.help/country/united-kingdom">\n ...## {xml_nodeset (5)}
## [1] <tr>\n<th>COUNTRY</th>\n <th>INFECTED</th>\ ...
## [2] <tr>\n<td><a href="https://corona.help/country/united-states">\n ...
## [3] <tr>\n<td><a href="https://corona.help/country/india">\n ...
## [4] <tr>\n<td><a href="https://corona.help/country/brazil">\n ...
## [5] <tr>\n<td><a href="https://corona.help/country/russia">\n ...## {xml_nodeset (1)}
## [1] <tr>\n<th>COUNTRY</th>\n <th>INFECTED</th>\ ...## {xml_nodeset (1)}
## [1] <tr>\n<th>COUNTRY</th>\n <th>INFECTED</th>\ ...
Let’s convert this to raw HTML using as.character() to practice writing regular expressions. Refer back to this output to help you determine what pattern you want to match:
# Convert rows to raw HTML
rows <- as.character(corona_rows)[-c(1)] # [-c(1)] means skip header row
# View first few rows as raw HTML
writeLines(head(rows, 2)) # printing via writeLines() is much prettier than printing via print()## <tr>
## <td><a href="https://corona.help/country/united-states">
## <div style="height:100%;width:100%">United States</div>
## </a></td>
## <td class="text-warning">22,132,045</td>
## <td class="text-warning text-bold-700">37,559</td>
## <td class="text-danger">374,124</td>
## <td class="text-danger text-bold-700">578</td>
## <td class="text-success">13,143,317</td>
## <td class="text-success text-bold-700">29,044</td>
## <td class="text-warning">8,614,604</td>
## <td class="text-danger">29,034</td>
## <td class="text-warning">265,444,863</td>
##
##
## </tr>
##
## <tr>
## <td><a href="https://corona.help/country/india">
## <div style="height:100%;width:100%">India</div>
## </a></td>
## <td class="text-warning">10,414,044</td>
## <td class="text-warning text-bold-700">0</td>
## <td class="text-danger">150,606</td>
## <td class="text-danger text-bold-700">0</td>
## <td class="text-success">10,036,722</td>
## <td class="text-success text-bold-700">0</td>
## <td class="text-warning">226,716</td>
## <td class="text-danger">8,944</td>
## <td class="text-warning">178,400,995</td>
##
##
## </tr>## [1] "character"## [1] "character"## [1] 225Example: Using
str_subset() to subset rows
Let’s filter for rows whose country name starts with 'United'. First, preview what our regular expression matches using str_view():
Inspect the output from str_detect(), which returns TRUE if there is a match and FALSE if not. For example, we see there is a TRUE for the first element (United States) and third element (United Kingdom):
## [1] TRUE FALSE FALSE FALSE TRUE FALSEFinally, subset rows by country name using str_subset(), which keeps elements of character vector for which str_detect() is TRUE (i.e., keeps elements where the pattern “matches”):
subset_by_country <- str_subset(string = rows, pattern = 'United \\w+')
writeLines(subset_by_country)## <tr>
## <td><a href="https://corona.help/country/united-states">
## <div style="height:100%;width:100%">United States</div>
## </a></td>
## <td class="text-warning">22,132,045</td>
## <td class="text-warning text-bold-700">37,559</td>
## <td class="text-danger">374,124</td>
## <td class="text-danger text-bold-700">578</td>
## <td class="text-success">13,143,317</td>
## <td class="text-success text-bold-700">29,044</td>
## <td class="text-warning">8,614,604</td>
## <td class="text-danger">29,034</td>
## <td class="text-warning">265,444,863</td>
##
##
## </tr>
##
## <tr>
## <td><a href="https://corona.help/country/united-kingdom">
## <div style="height:100%;width:100%">United Kingdom</div>
## </a></td>
## <td class="text-warning">2,898,052</td>
## <td class="text-warning text-bold-700">18</td>
## <td class="text-danger">78,632</td>
## <td class="text-danger text-bold-700">0</td>
## <td class="text-success">1,364,821</td>
## <td class="text-success text-bold-700">0</td>
## <td class="text-warning">1,454,599</td>
## <td class="text-danger">2,821</td>
## <td class="text-warning">58,231,730</td>
##
##
## </tr>
##
## <tr>
## <td><a href="https://corona.help/country/united-arab-emirates">
## <div style="height:100%;width:100%">United Arab Emirates</div>
## </a></td>
## <td class="text-warning">221,754</td>
## <td class="text-warning text-bold-700">0</td>
## <td class="text-danger">694</td>
## <td class="text-danger text-bold-700">0</td>
## <td class="text-success">199,178</td>
## <td class="text-success text-bold-700">0</td>
## <td class="text-warning">21,882</td>
## <td class="text-danger">0</td>
## <td class="text-warning">21,903,309</td>
##
##
## </tr>Example: Using
str_extract() to extract link for each row
Since all links follow the same pattern, we can use regex to extract this info:
links <- str_extract(string = rows, pattern = 'https://corona.help/country/[-a-z]+')
# View first few links
head(links)## [1] "https://corona.help/country/united-states"
## [2] "https://corona.help/country/india"
## [3] "https://corona.help/country/brazil"
## [4] "https://corona.help/country/russia"
## [5] "https://corona.help/country/united-kingdom"
## [6] "https://corona.help/country/france"Example: Using
str_match() to extract country for each row
Since all countries are in a div element with the same attributes, we can use the following regex to extract the country name:
countries <- str_match(string = rows, pattern = '<div style="height:100%;width:100%">([\\w ]+)</div>')
# View first few countries
# We used a capturing group to extract the country name from between the tags
head(countries)## [,1]
## [1,] "<div style=\"height:100%;width:100%\">United States</div>"
## [2,] "<div style=\"height:100%;width:100%\">India</div>"
## [3,] "<div style=\"height:100%;width:100%\">Brazil</div>"
## [4,] "<div style=\"height:100%;width:100%\">Russia</div>"
## [5,] "<div style=\"height:100%;width:100%\">United Kingdom</div>"
## [6,] "<div style=\"height:100%;width:100%\">France</div>"
## [,2]
## [1,] "United States"
## [2,] "India"
## [3,] "Brazil"
## [4,] "Russia"
## [5,] "United Kingdom"
## [6,] "France"Example: Using
str_match_all() to extract number deaths and critical for each row
Since both the number of deaths and critical are in a <td> element with the same class attribute, we can use the following regex to extract both numbers:
num_danger <- str_match_all(string = rows, pattern = '<td class="text-danger">([\\d,]+)</td>')
# View matches for first few rows
# We used a capturing group to extract the numbers from between the tags
head(num_danger)## [[1]]
## [,1] [,2]
## [1,] "<td class=\"text-danger\">374,124</td>" "374,124"
## [2,] "<td class=\"text-danger\">29,034</td>" "29,034"
##
## [[2]]
## [,1] [,2]
## [1,] "<td class=\"text-danger\">150,606</td>" "150,606"
## [2,] "<td class=\"text-danger\">8,944</td>" "8,944"
##
## [[3]]
## [,1] [,2]
## [1,] "<td class=\"text-danger\">200,498</td>" "200,498"
## [2,] "<td class=\"text-danger\">8,318</td>" "8,318"
##
## [[4]]
## [,1] [,2]
## [1,] "<td class=\"text-danger\">60,457</td>" "60,457"
## [2,] "<td class=\"text-danger\">2,300</td>" "2,300"
##
## [[5]]
## [,1] [,2]
## [1,] "<td class=\"text-danger\">78,632</td>" "78,632"
## [2,] "<td class=\"text-danger\">2,821</td>" "2,821"
##
## [[6]]
## [,1] [,2]
## [1,] "<td class=\"text-danger\">66,841</td>" "66,841"
## [2,] "<td class=\"text-danger\">2,616</td>" "2,616"Example: Using
str_replace_all() to convert numeric values to thousands for each row
Rewrite all numeric values greater than one thousand in terms of k:
num_to_k <- str_replace_all(string = rows, pattern = '>([\\d,]+),\\d{3}<', replacement = '>\\1k<')
# View replacements for first few rows
writeLines(head(num_to_k))## <tr>
## <td><a href="https://corona.help/country/united-states">
## <div style="height:100%;width:100%">United States</div>
## </a></td>
## <td class="text-warning">22,132k</td>
## <td class="text-warning text-bold-700">37k</td>
## <td class="text-danger">374k</td>
## <td class="text-danger text-bold-700">578</td>
## <td class="text-success">13,143k</td>
## <td class="text-success text-bold-700">29k</td>
## <td class="text-warning">8,614k</td>
## <td class="text-danger">29k</td>
## <td class="text-warning">265,444k</td>
##
##
## </tr>
##
## <tr>
## <td><a href="https://corona.help/country/india">
## <div style="height:100%;width:100%">India</div>
## </a></td>
## <td class="text-warning">10,414k</td>
## <td class="text-warning text-bold-700">0</td>
## <td class="text-danger">150k</td>
## <td class="text-danger text-bold-700">0</td>
## <td class="text-success">10,036k</td>
## <td class="text-success text-bold-700">0</td>
## <td class="text-warning">226k</td>
## <td class="text-danger">8k</td>
## <td class="text-warning">178,400k</td>
##
##
## </tr>
##
## <tr>
## <td><a href="https://corona.help/country/brazil">
## <div style="height:100%;width:100%">Brazil</div>
## </a></td>
## <td class="text-warning">7,961k</td>
## <td class="text-warning text-bold-700">0</td>
## <td class="text-danger">200k</td>
## <td class="text-danger text-bold-700">0</td>
## <td class="text-success">7,096k</td>
## <td class="text-success text-bold-700">0</td>
## <td class="text-warning">664k</td>
## <td class="text-danger">8k</td>
## <td class="text-warning">28,600k</td>
##
##
## </tr>
##
## <tr>
## <td><a href="https://corona.help/country/russia">
## <div style="height:100%;width:100%">Russia</div>
## </a></td>
## <td class="text-warning">3,332k</td>
## <td class="text-warning text-bold-700">0</td>
## <td class="text-danger">60k</td>
## <td class="text-danger text-bold-700">0</td>
## <td class="text-success">2,709k</td>
## <td class="text-success text-bold-700">0</td>
## <td class="text-warning">562k</td>
## <td class="text-danger">2k</td>
## <td class="text-warning">92,600k</td>
##
##
## </tr>
##
## <tr>
## <td><a href="https://corona.help/country/united-kingdom">
## <div style="height:100%;width:100%">United Kingdom</div>
## </a></td>
## <td class="text-warning">2,898k</td>
## <td class="text-warning text-bold-700">18</td>
## <td class="text-danger">78k</td>
## <td class="text-danger text-bold-700">0</td>
## <td class="text-success">1,364k</td>
## <td class="text-success text-bold-700">0</td>
## <td class="text-warning">1,454k</td>
## <td class="text-danger">2k</td>
## <td class="text-warning">58,231k</td>
##
##
## </tr>
##
## <tr>
## <td><a href="https://corona.help/country/france">
## <div style="height:100%;width:100%">France</div>
## </a></td>
## <td class="text-warning">2,727k</td>
## <td class="text-warning text-bold-700">0</td>
## <td class="text-danger">66k</td>
## <td class="text-danger text-bold-700">0</td>
## <td class="text-success">198k</td>
## <td class="text-success text-bold-700">0</td>
## <td class="text-warning">2,461k</td>
## <td class="text-danger">2k</td>
## <td class="text-warning">36,890k</td>
##
##
## </tr>12 Appendix
12.1 rtweet package
rtweet package (from rtweet website)
All you need is a Twitter account (user name and password) and you can be up in running in minutes!
Simply send a request to Twitter’s API (with a function like search_tweets(), get_timeline(), get_followers(), get_favorites(), etc.) during an interactive session of R, authorize the embedded rstats2twitter app (approve the browser popup), and your token will be created and saved/stored (for future sessions) for you!
- This package allows users to interact with Twitter’s REST and stream APIs.
12.1.1 search_tweets function
rtweet documentation (from CRAN)
- In the following weeks we will get an opportunity to interact more with the rtweet package and explore other
rwteetfunctions. For now, let’s focus on thesearch_tweetsfunction.
search_tweets(): Get tweets data on statuses identified via search query.
Description
- Returns Twitter statuses matching a user provided search query. ONLY RETURNS DATA FROM THE PAST 6-9 DAYS. To return more than 18,000 statuses in a single call, set “retryonratelimit” to TRUE. search_tweets2 Passes all arguments to search_tweets. Returns data from one OR MORE search queries.
Usage
search_tweets(q, n = 100, type = “recent”, include_rts = TRUE, geocode = NULL, max_id = NULL, parse = TRUE, token = NULL, retryonratelimit = FALSE, verbose = TRUE, … )`
Arguments
q: Query to be searched, used to filter and select tweets to return from Twitter’s REST API. Must be a character string not to exceed maximum of 500 characters. Spaces behave like boolean “AND” operator. To search for tweets containing at least one of multiple possible terms, separate each search term with spaces and “OR” (in caps). For example, the search q = “data science” looks for tweets containing both “data” and “science” located anywhere in the tweets and in any order. When “OR” is entered between search terms, query = “data OR science”, Twitter’s REST API should return any tweet that contains either “data” or “science.” It is also possible to search for exact phrases using double quotes. To do this, either wrap single quotes around a search query using double quotes, e.g., q = ‘“data science”’ or escape each internal double quote with a single backslash, e.g., q = “"data science"”. Some other useful query tips:- Exclude retweets via “-filter:retweets”
- Exclude quotes via “-filter:quote”
- Exclude replies via “-filter:replies”
- Filter (return only) verified via “filter:verified”
- Exclude verified via “-filter:verified”
- Get everything (firehose for free) via “-filter:verified OR filter:verified”
- Filter (return only) tweets with links to news articles via “filter:news”
- Filter (return only) tweets with media “filter:media”
n: Integer, specifying the total number of desired tweets to return. Defaults to 100. Maximum number of tweets returned from a single token is 18,000. To return more than 18,000 tweets, users are encouraged to set retryonratelimit to TRUE. See details for more information.type: Character string specifying which type of search results to return from Twitter’s REST API. The current default is type = “recent”, other valid types include type = “mixed” and type = “popular”.include_rts: Logical, indicating whether to include retweets in search results. Retweets are classified as any tweet generated by Twitter’s built-in “retweet” (recycle arrows) function. These are distinct from quotes (retweets with additional text provided from sender) or manual retweets (old school method of manually entering “RT” into the text of one’s tweets).geocode: Geographical limiter of the template “latitude,longitude,radius” e.g., geocode = “37.78,-122.40,1mi”.max_id: Character, returns results with an ID less than (that is, older than) or equal to ‘max_id‘. Especially useful for large data returns that require multiple iterations interrupted by user time constraints. For searches exceeding 18,000 tweets, users are encouraged to take advantage of rtweet’s internal automation procedures for waiting on rate limits by setting retryonratelimit argument to TRUE. It some cases, it is possible that due to processing time and rate limits, retrieving several million tweets can take several hours or even multiple days. In these cases, it would likely be useful to leverage retryonratelimit for sets of tweets and max_id to allow results to continue where previous efforts left off.parse: Logical, indicating whether to return parsed data.frame, if true, or nested list, if false. By default, parse = TRUE saves users from the wreck of time and frustration associated with disentangling the nasty nested list returned from Twitter’s API. As Twitter’s APIs are subject to change, this argument would be especially useful when changes to Twitter’s APIs affect performance of internal parsers. Setting parse = FALSE also ensures the maximum amount of possible information is returned. By default, the rtweet parse process returns nearly all bits of information returned from Twitter. However, users may occasionally encounter new or omitted variables. In these rare cases, the nested list object will be the only way to access these variables.token: Every user should have their own Oauth (Twitter API) token. By default token = NULL this function looks for the path to a saved Twitter token via environment variables (which is what ‘create_token()‘ sets up by default during initial token creation). For instruction on how to create a Twitter token see the tokens vignette, i.e., ‘vignettes(“auth”, “rtweet”)‘ or see ?tokens.retryonratelimit: Logical indicating whether to wait and retry when rate limited. This argument is only relevant if the desired return (n) exceeds the remaining limit of available requests (assuming no other searches have been conducted in the past 15 minutes, this limit is 18,000 tweets). Defaults to false. Set to TRUE to automate process of conducting big searches (i.e., n > 18000). For many search queries, esp. specific or specialized searches, there won’t be more than 18,000 tweets to return. But for broad, generic, or popular topics, the total number of tweets within the REST window of time (7-10 days) can easily reach the millions.verbose: Logical, indicating whether or not to include output processing/retrieval messages. Defaults to TRUE. For larger searches, messages include rough estimates for time remaining between searches. It should be noted, however, that these time estimates only describe the amount of time between searches and not the total time remaining. For large searches conducted with retryonratelimit set to TRUE, the estimated retrieval time can be estimated by dividing the number of requested tweets by 18,000 and then multiplying the quotient by 15 (token reset time, in minutes)....: Further arguments passed as query parameters in request sent to Twitter’s REST API. To return only English language tweets, for example, use lang = “en”. For more options see Twitter’s API documentation.
12.1.2 search_tweets example
#load packages
library(tidyverse)
#install.packages("rtweet")
library(rtweet)
#Create an object called p12 that is a vector of pac 12 admissions Twitter handles
p12 <- c("uaadmissions", "FutureSunDevils", "caladmissions", "UCLAAdmission",
"futurebuffs", "uoregon", "BeaverVIP", "USCAdmission",
"engagestanford", "UtahAdmissions", "UW", "WSUPullman")
#Use search_tweets to load 500 tweets using the p12 object
p12_full_df <- search_tweets(paste0("from:", p12, collapse = " OR "), n = 500)
#saveRDS(p12_full_df, "p12_dataset.RDS")12.2 RegExplain Addin
Regular expressions are tricky. RegExplain makes it easier to see what you’re doing.
RegExplain is an RStudio addin that allows the user to check their regex matching functions interactively.
Credit: Garrick Aden-Buie (RegExplain)
Installation